Stable marriage problem

From Rosetta Code
Task
Stable marriage problem
You are encouraged to solve this task according to the task description, using any language you may know.

Solve the Stable marriage problem using the Gale/Shapley algorithm.


Problem description
Given an equal number of men and women to be paired for marriage, each man ranks all the women in order of his preference and each woman ranks all the men in order of her preference.

A stable set of engagements for marriage is one where no man prefers a woman over the one he is engaged to, where that other woman also prefers that man over the one she is engaged to. I.e. with consulting marriages, there would be no reason for the engagements between the people to change.

Gale and Shapley proved that there is a stable set of engagements for any set of preferences and the first link above gives their algorithm for finding a set of stable engagements.


Task Specifics
Given ten males:

   abe, bob, col, dan, ed, fred, gav, hal, ian, jon

And ten females:

   abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan

And a complete list of ranked preferences, where the most liked is to the left:

  abe: abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay
  bob: cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay
  col: hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan
  dan: ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi
   ed: jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay
 fred: bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay
  gav: gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay
  hal: abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee
  ian: hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve
  jon: abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope
   
  abi: bob, fred, jon, gav, ian, abe, dan, ed, col, hal
  bea: bob, abe, col, fred, gav, dan, ian, ed, jon, hal
 cath: fred, bob, ed, gav, hal, col, ian, abe, dan, jon
  dee: fred, jon, col, abe, ian, hal, gav, dan, bob, ed
  eve: jon, hal, fred, dan, abe, gav, col, ed, ian, bob
  fay: bob, abe, ed, ian, jon, dan, fred, gav, col, hal
  gay: jon, gav, hal, fred, bob, abe, col, ed, dan, ian
 hope: gav, jon, bob, abe, ian, dan, hal, ed, col, fred
  ivy: ian, col, hal, gav, fred, bob, abe, ed, jon, dan
  jan: ed, hal, gav, abe, bob, jon, col, ian, fred, dan
  1. Use the Gale Shapley algorithm to find a stable set of engagements
  2. Perturb this set of engagements to form an unstable set of engagements then check this new set for stability.


References

  1. The Stable Marriage Problem. (Eloquent description and background information).
  2. Gale-Shapley Algorithm Demonstration.
  3. Another Gale-Shapley Algorithm Demonstration.
  4. Stable Marriage Problem - Numberphile (Video).
  5. Stable Marriage Problem (the math bit) (Video).
  6. The Stable Marriage Problem and School Choice. (Excellent exposition)



AutoHotkey

Works with: AutoHotkey L

<lang autohotkey>; Given a complete list of ranked preferences, where the most liked is to the left: abe := ["abi", "eve", "cath", "ivy", "jan", "dee", "fay", "bea", "hope", "gay"] bob := ["cath", "hope", "abi", "dee", "eve", "fay", "bea", "jan", "ivy", "gay"] col := ["hope", "eve", "abi", "dee", "bea", "fay", "ivy", "gay", "cath", "jan"] dan := ["ivy", "fay", "dee", "gay", "hope", "eve", "jan", "bea", "cath", "abi"] ed := ["jan", "dee", "bea", "cath", "fay", "eve", "abi", "ivy", "hope", "gay"] fred := ["bea", "abi", "dee", "gay", "eve", "ivy", "cath", "jan", "hope", "fay"] gav := ["gay", "eve", "ivy", "bea", "cath", "abi", "dee", "hope", "jan", "fay"] hal := ["abi", "eve", "hope", "fay", "ivy", "cath", "jan", "bea", "gay", "dee"] ian := ["hope", "cath", "dee", "gay", "bea", "abi", "fay", "ivy", "jan", "eve"] jon := ["abi", "fay", "jan", "gay", "eve", "bea", "dee", "cath", "ivy", "hope"] abi := ["bob", "fred", "jon", "gav", "ian", "abe", "dan", "ed", "col", "hal"] bea := ["bob", "abe", "col", "fred", "gav", "dan", "ian", "ed", "jon", "hal"] cath := ["fred", "bob", "ed", "gav", "hal", "col", "ian", "abe", "dan", "jon"] dee := ["fred", "jon", "col", "abe", "ian", "hal", "gav", "dan", "bob", "ed"] eve := ["jon", "hal", "fred", "dan", "abe", "gav", "col", "ed", "ian", "bob"] fay := ["bob", "abe", "ed", "ian", "jon", "dan", "fred", "gav", "col", "hal"] gay := ["jon", "gav", "hal", "fred", "bob", "abe", "col", "ed", "dan", "ian"] hope := ["gav", "jon", "bob", "abe", "ian", "dan", "hal", "ed", "col", "fred"] ivy := ["ian", "col", "hal", "gav", "fred", "bob", "abe", "ed", "jon", "dan"] jan := ["ed", "hal", "gav", "abe", "bob", "jon", "col", "ian", "fred", "dan"]

of ten males

males := ["abe", "bob", "col", "dan", "ed", "fred", "gav", "hal", "ian", "jon"]

and ten females

females := ["abi", "bea", "cath", "dee", "eve", "fay", "gay", "hope", "ivy", "jan"]

and an empty set of engagements

engagements := Object() freemales := males.Clone() ,s := "Engagements:`n"

use the Gale Shapley algorithm to find a stable set of engagements

For i, male in freemales ; i=index of male (not needed) { j:=1 ; index of female While (engagements[female:=%male%[j]] != "" and index(%female%, male) > index(%female%, engagements[female])) j++ ; each male loops through all females in order of his preference until one accepts him If (engagements[female] != "") ; if she was previously engaged freemales.insert(engagements[female]) ; her old male goes to the bottom of the list ,s .= female . " dumped " . engagements[female] . "`n" engagements[female] := male ; the new engagement is registered ,s .= female . " accepted " . male . "`n" }

summarize results

s .= "`nCouples:`n" For female, male in engagements s .= female . " is engaged to " . male . "`n" s .= Stable(engagements, females)

then perturb this set of engagements to form an unstable set of engagements then check this new set for stability

s .= "`nWhat if cath and ivy swap?`n" engagements["cath"]:="abe", engagements["ivy"]:="bob"

summarize results

s .= "`nCouples:`n" For female, male in engagements s .= female . " is engaged to " . male . "`n" s .= Stable(engagements, females)

Msgbox % clipboard := s Return

Functions

Index(obj, value) { For key, val in obj If (val = value) Return, key, ErrorLevel := 0 Return, False, Errorlevel := 1 }

Stable(engagements, females) { For female, male in engagements { For j, female2 in females ; j=index of female (not needed) { If (index(%male%, female) > index(%male%, female2) and index(%female2%, male2:=engagements[female2]) > index(%female2%, male)) s .= male . " is engaged to " . female . " but would prefer " . female2 . " and " . female2 . " is engaged to " . male2 . " but would prefer " . male . "`n" } } If s Return "`nThese couples are not stable.`n" . s Else Return "`nThese couples are stable.`n" }</lang>

Output:
Engagements:
abi accepted abe
cath accepted bob
hope accepted col
ivy accepted dan
jan accepted ed
bea accepted fred
gay accepted gav
eve accepted hal
hope dumped col
hope accepted ian
abi dumped abe
abi accepted jon
dee accepted col
ivy dumped dan
ivy accepted abe
fay accepted dan

Couples:
abi is engaged to jon
bea is engaged to fred
cath is engaged to bob
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to abe
jan is engaged to ed

These couples are stable.

What if cath and ivy swap?

Couples:
abi is engaged to jon
bea is engaged to fred
cath is engaged to abe
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to bob
jan is engaged to ed

These couples are not stable.
bob is engaged to ivy but would prefer abi and abi is engaged to jon but would prefer bob
bob is engaged to ivy but would prefer bea and bea is engaged to fred but would prefer bob
bob is engaged to ivy but would prefer cath and cath is engaged to abe but would prefer bob
bob is engaged to ivy but would prefer fay and fay is engaged to dan but would prefer bob
bob is engaged to ivy but would prefer hope and hope is engaged to ian but would prefer bob

Batch File

<lang dos>@echo off setlocal enabledelayedexpansion

%== Initialization ==% set "male= abe bob col dan ed fred gav hal ian jon" ::First whitespace is necessary set "female= abi bea cath dee eve fay gay hope ivy jan" ::same here...

::Initialization of pseudo-arrays [Male] set "cnt=0" & for %%. in (abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay) do (set abe[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay) do (set bob[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan) do (set col[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi) do (set dan[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay) do (set ed[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay) do (set fred[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay) do (set gav[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee) do (set hal[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve) do (set ian[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope) do (set jon[!cnt!]=%%.&set /a cnt+=1)

::Initialization of pseudo-arrays [Female] set "cnt=0" & for %%. in (bob, fred, jon, gav, ian, abe, dan, ed, col, hal) do (set abi[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (bob, abe, col, fred, gav, dan, ian, ed, jon, hal) do (set bea[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (fred, bob, ed, gav, hal, col, ian, abe, dan, jon) do (set cath[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (fred, jon, col, abe, ian, hal, gav, dan, bob, ed) do (set dee[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (jon, hal, fred, dan, abe, gav, col, ed, ian, bob) do (set eve[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (bob, abe, ed, ian, jon, dan, fred, gav, col, hal) do (set fay[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (jon, gav, hal, fred, bob, abe, col, ed, dan, ian) do (set gay[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (gav, jon, bob, abe, ian, dan, hal, ed, col, fred) do (set hope[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (ian, col, hal, gav, fred, bob, abe, ed, jon, dan) do (set ivy[!cnt!]=%%.&set /a cnt+=1) set "cnt=0" & for %%. in (ed, hal, gav, abe, bob, jon, col, ian, fred, dan) do (set jan[!cnt!]=%%.&set /a cnt+=1) %==/Initialization ==%

( %== The main thing ==% echo.HISTORY: call :stableMatching echo. echo.NEWLYWEDS: call :display echo. call :isStable echo. echo.What if ed and hal swapped? call :swapper ed hal echo. echo.NEW-NEWLYWEDS: call :display echo. call :isStable pause>nul exit /b 0 ) %==/The main thing ==%

%== The algorithm ==%

stableMatching

set "free_men=%male%" ::The free-men variable set "free_women=%female%" ::The free-women variable set nextgirl=0

thematchloop

set m=&for %%F in (!free_men!) do (if not defined m set "m=%%F") if "!m!"=="" goto :EOF

for /f "tokens=1-2 delims==" %%A in ('set !m![!nextgirl!]') do set "w=%%B" set "propo=" for %%W in (!free_women!) do ( if "%%W"=="!w!" ( set propo=TRUE set "!w!_=!m!" & set "!m!_=!w!" set free_women=!free_women: %w%=! set free_men=!free_men: %m%=! echo. !w! ACCEPTED !m!. ) ) if defined propo (set "nextgirl=0" & goto thematchloop)

for /f "tokens=1-2 delims==" %%A in ('set !w!_') do set "mbef=%%B" set "replace=" & for /f "tokens=1-2 delims==" %%R in ('set !w![') do ( if not defined replace ( if "%%S"=="!m!" ( set replace=TRUE set "!w!_=!m!" & set "!m!_=!w!" set "free_men=!free_men! !mbef!" set "free_men=!free_men: %m%=!" set nextgirl=0 echo. !w! LEFT !mbef!. echo. !w! ACCEPTED !m!. ) if "%%S"=="!mbef!" ( set /a nextgirl+=1 set replace=FALSE ) ) ) goto thematchloop %==/The Algorithm ==%

%== Output the Couples ==%

display

for %%S in (!male!) do echo. %%S and !%%S_!. goto :EOF %==/Output the Couples ==%

%== Stability Checking ==%

isStable

for %%M in (!female!) do ( set "better=" set "dislike=" & for /f "tokens=1-2 delims==" %%R in ('set %%M[') do ( if not defined dislike ( if "%%S"=="!%%M_!" (set dislike=T) else (set "better=!better! %%S") ) ) for %%X in (!better!) do ( for /f "tokens=1-2 delims==" %%F in ('set %%X_') do set curr_partner_of_boy=%%G set "main_check=" for /f "tokens=1-2 delims==" %%B in ('set %%X[') do ( if not defined main_check ( if "%%C"=="%%M" ( echo.STABILITY = FALSE. echo %%M and %%X would rather be together than their current partners. goto :EOF ) if "%%C"=="!curr_partner_of_boy!" set "main_check=CONTINUE" ) ) ) ) echo.STABILITY = TRUE. goto :EOF %==/Stability Chacking ==%

%== Swapper ==%

swapper

set %~1.tmp=!%~1_! set %~2.tmp=!%~2_! set "%~1_=!%~2.tmp!" set "%~2_=!%~1.tmp!" set "!%~1.tmp!_=%~2" set "!%~2.tmp!_=%~1" goto :EOF %==/Swapper==%</lang>

Output:
HISTORY:
        abi ACCEPTED abe.
        cath ACCEPTED bob.
        hope ACCEPTED col.
        ivy ACCEPTED dan.
        jan ACCEPTED ed.
        bea ACCEPTED fred.
        gay ACCEPTED gav.
        eve ACCEPTED hal.
        hope LEFT col.
        hope ACCEPTED ian.
        abi LEFT abe.
        abi ACCEPTED jon.
        dee ACCEPTED col.
        ivy LEFT dan.
        ivy ACCEPTED abe.
        fay ACCEPTED dan.

NEWLYWEDS:
        abe and ivy.
        bob and cath.
        col and dee.
        dan and fay.
        ed and jan.
        fred and bea.
        gav and gay.
        hal and eve.
        ian and hope.
        jon and abi.

STABILITY = TRUE.

What if ed and hal swapped?

NEW-NEWLYWEDS:
        abe and ivy.
        bob and cath.
        col and dee.
        dan and fay.
        ed and eve.
        fred and bea.
        gav and gay.
        hal and jan.
        ian and hope.
        jon and abi.

STABILITY = FALSE.
eve and hal would rather be together than their current partners.

BBC BASIC

<lang bbcbasic> N = 10

     DIM mname$(N), wname$(N), mpref$(N), wpref$(N), mpartner%(N), wpartner%(N)
     DIM proposed&(N,N)
     mname$() = "", "Abe","Bob","Col","Dan","Ed","Fred","Gav","Hal","Ian","Jon"
     wname$() = "", "Abi","Bea","Cath","Dee","Eve","Fay","Gay","Hope","Ivy","Jan"
     mpref$() = "", "AECIJDFBHG","CHADEFBJIG","HEADBFIGCJ","IFDGHEJBCA","JDBCFEAIHG",\
     \              "BADGEICJHF","GEIBCADHJF","AEHFICJBGD","HCDGBAFIJE","AFJGEBDCIH"
     wpref$() = "", "BFJGIADECH","BACFGDIEJH","FBEGHCIADJ","FJCAIHGDBE","JHFDAGCEIB",\
     \              "BAEIJDFGCH","JGHFBACEDI","GJBAIDHECF","ICHGFBAEJD","EHGABJCIFD"
     
     REM The Gale-Shapley algorithm:
     REPEAT
       FOR m% = 1 TO N
         REPEAT
           IF mpartner%(m%) EXIT REPEAT
           FOR i% = 1 TO N
             w% = ASCMID$(mpref$(m%),i%) - 64
             IF proposed&(m%,w%) = 0 EXIT FOR
           NEXT i%
           IF i% > N EXIT REPEAT
           proposed&(m%,w%) = 1
           IF wpartner%(w%) = 0 THEN
             mpartner%(m%) = w% : REM Get engaged
             wpartner%(w%) = m%
           ELSE
             o% = wpartner%(w%)
             IF INSTR(wpref$(w%), LEFT$(mname$(m%),1)) < \
             \  INSTR(wpref$(w%), LEFT$(mname$(o%),1)) THEN
               mpartner%(o%) = 0  : REM Split up
               mpartner%(m%) = w% : REM Get engaged
               wpartner%(w%) = m%
             ENDIF
           ENDIF
         UNTIL TRUE
       NEXT m%
     UNTIL SUM(mpartner%()) = (N*(N+1))/2
     
     FOR m% = 1 TO N
       PRINT mname$(m%) " is engaged to " wname$(mpartner%(m%))
     NEXT
     PRINT "Relationships are ";
     IF FNstable PRINT "stable." ELSE PRINT "unstable."
     
     a% = RND(N)
     REPEAT b% = RND(N) : UNTIL b%<>a%
     PRINT '"Now swapping " mname$(a%) "'s and " mname$(b%) "'s partners:"
     SWAP mpartner%(a%), mpartner%(b%)
     PRINT mname$(a%) " is engaged to " wname$(mpartner%(a%))
     PRINT mname$(b%) " is engaged to " wname$(mpartner%(b%))
     PRINT "Relationships are ";
     IF FNstable PRINT "stable." ELSE PRINT "unstable."
     END
     
     DEF FNstable
     LOCAL m%, w%, o%, p%
     FOR m% = 1 TO N
       w% = mpartner%(m%)
       FOR o% = 1 TO N
         p% = wpartner%(o%)
         IF INSTR(mpref$(m%), LEFT$(wname$(o%),1)) < \
         \  INSTR(mpref$(m%), LEFT$(wname$(w%),1)) AND \
         \  INSTR(wpref$(o%), LEFT$(mname$(m%),1)) < \
         \  INSTR(wpref$(o%), LEFT$(mname$(p%),1)) THEN
           = FALSE
         ENDIF
       NEXT o%
     NEXT m%
     = TRUE</lang>

Output:

Abe is engaged to Ivy
Bob is engaged to Cath
Col is engaged to Dee
Dan is engaged to Fay
Ed is engaged to Jan
Fred is engaged to Bea
Gav is engaged to Gay
Hal is engaged to Eve
Ian is engaged to Hope
Jon is engaged to Abi
Relationships are stable.

Now swapping Hal's and Ian's partners:
Hal is engaged to Hope
Ian is engaged to Eve
Relationships are unstable.

Bracmat

<lang bracmat>( (abe.abi eve cath ivy jan dee fay bea hope gay)

     (bob.cath hope abi dee eve fay bea jan ivy gay)
     (col.hope eve abi dee bea fay ivy gay cath jan)
     (dan.ivy fay dee gay hope eve jan bea cath abi)
     (ed.jan dee bea cath fay eve abi ivy hope gay)
     (fred.bea abi dee gay eve ivy cath jan hope fay)
     (gav.gay eve ivy bea cath abi dee hope jan fay)
     (hal.abi eve hope fay ivy cath jan bea gay dee)
     (ian.hope cath dee gay bea abi fay ivy jan eve)
     (jon.abi fay jan gay eve bea dee cath ivy hope)
 : ?Mplan
 : ?M

& (abi.bob fred jon gav ian abe dan ed col hal)

     (bea.bob abe col fred gav dan ian ed jon hal)
     (cath.fred bob ed gav hal col ian abe dan jon)
     (dee.fred jon col abe ian hal gav dan bob ed)
     (eve.jon hal fred dan abe gav col ed ian bob)
     (fay.bob abe ed ian jon dan fred gav col hal)
     (gay.jon gav hal fred bob abe col ed dan ian)
     (hope.gav jon bob abe ian dan hal ed col fred)
     (ivy.ian col hal gav fred bob abe ed jon dan)
     (jan.ed hal gav abe bob jon col ian fred dan)
 : ?W

& :?engaged & whl

 ' (   !Mplan
     :   ?A
         (?m&~(!engaged:? (!m.?) ?).%?w ?ws)
         ( ?Z
         & (   (   ~(!engaged:?a (?m`.!w) ?z)
                 & (!m.!w) !engaged
               |   !W:? (!w.? !m ? !m` ?) ?
                 & !a (!m.!w) !z
               )
             : ?engaged
           | 
           )
         & !Z !A (!m.!ws):?Mplan
         )
   )

& ( unstable

 =   m1 m2 w1 w2
   .   !arg
     :   ?
         (?m1.?w1)
         ?
         (?m2.?w2)
         ( ?
         & (   !M:? (!m1.? !w2 ? !w1 ?) ?
             & !W:? (!w2.? !m1 ? !m2 ?) ?
           |   !M:? (!m2.? !w1 ? !w2 ?) ?
             & !W:? (!w1.? !m2 ? !m1 ?) ?
           )
         )
 )

& ( unstable$!engaged&out$unstable

 | out$stable
 )

& out$!engaged & !engaged:(?m1.?w1) (?m2.?w2) ?others & out$(swap !w1 for !w2) & ( unstable$((!m1.!w2) (!m2.!w1) !others)

   & out$unstable
 | out$stable
 )

);</lang>

Output:
stable
  (dan.fay)
  (col.dee)
  (hal.eve)
  (gav.gay)
  (fred.bea)
  (ed.jan)
  (abe.ivy)
  (ian.hope)
  (bob.cath)
  (jon.abi)
swap fay for dee
unstable

C

Oddly enough (or maybe it should be that way, only that I don't know): if the women were proposing instead of the men, the resulting pairs are exactly the same. <lang C>#include <stdio.h>

int verbose = 0; enum { clown = -1, abe, bob, col, dan, ed, fred, gav, hal, ian, jon, abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan, }; const char *name[] = { "Abe", "Bob", "Col", "Dan", "Ed", "Fred", "Gav", "Hal", "Ian", "Jon", "Abi", "Bea", "Cath", "Dee", "Eve", "Fay", "Gay", "Hope", "Ivy", "Jan" }; int pref[jan + 1][jon + 1] = { { abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay }, { cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay }, { hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan }, { ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi }, { jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay }, { bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay }, { gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay }, { abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee }, { hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve }, { abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope },

{ bob, fred, jon, gav, ian, abe, dan, ed, col, hal }, { bob, abe, col, fred, gav, dan, ian, ed, jon, hal }, { fred, bob, ed, gav, hal, col, ian, abe, dan, jon }, { fred, jon, col, abe, ian, hal, gav, dan, bob, ed }, { jon, hal, fred, dan, abe, gav, col, ed, ian, bob }, { bob, abe, ed, ian, jon, dan, fred, gav, col, hal }, { jon, gav, hal, fred, bob, abe, col, ed, dan, ian }, { gav, jon, bob, abe, ian, dan, hal, ed, col, fred }, { ian, col, hal, gav, fred, bob, abe, ed, jon, dan }, { ed, hal, gav, abe, bob, jon, col, ian, fred, dan }, }; int pairs[jan + 1], proposed[jan + 1];

void engage(int man, int woman) { pairs[man] = woman; pairs[woman] = man; if (verbose) printf("%4s is engaged to %4s\n", name[man], name[woman]); }

void dump(int woman, int man) { pairs[man] = pairs[woman] = clown; if (verbose) printf("%4s dumps %4s\n", name[woman], name[man]); }

/* how high this person ranks that: lower is more preferred */ int rank(int this, int that) { int i; for (i = abe; i <= jon && pref[this][i] != that; i++); return i; }

void propose(int man, int woman) { int fiance = pairs[woman]; if (verbose) printf("%4s proposes to %4s\n", name[man], name[woman]);

if (fiance == clown) { engage(man, woman); } else if (rank(woman, man) < rank(woman, fiance)) { dump(woman, fiance); engage(man, woman); } }

int covet(int man1, int wife2) { if (rank(man1, wife2) < rank(man1, pairs[man1]) && rank(wife2, man1) < rank(wife2, pairs[wife2])) { printf( " %4s (w/ %4s) and %4s (w/ %4s) prefer each other" " over current pairing.\n", name[man1], name[pairs[man1]], name[wife2], name[pairs[wife2]] ); return 1; } return 0; }

int thy_neighbors_wife(int man1, int man2) { /* +: force checking all pairs; "||" would shortcircuit */ return covet(man1, pairs[man2]) + covet(man2, pairs[man1]); }

int unstable() { int i, j, bad = 0; for (i = abe; i < jon; i++) { for (j = i + 1; j <= jon; j++) if (thy_neighbors_wife(i, j)) bad = 1; } return bad; }

int main() { int i, unengaged; /* init: everyone marries the clown */ for (i = abe; i <= jan; i++) pairs[i] = proposed[i] = clown;

/* rounds */ do { unengaged = 0; for (i = abe; i <= jon; i++) { //for (i = abi; i <= jan; i++) { /* could let women propose */ if (pairs[i] != clown) continue; unengaged = 1; propose(i, pref[i][++proposed[i]]); } } while (unengaged);

printf("Pairing:\n"); for (i = abe; i <= jon; i++) printf(" %4s - %s\n", name[i], pairs[i] == clown ? "clown" : name[pairs[i]]);

printf(unstable() ? "Marriages not stable\n" /* draw sad face here */ : "Stable matchup\n");

printf("\nBut if Bob and Fred were to swap:\n"); i = pairs[bob]; engage(bob, pairs[fred]); engage(fred, i); printf(unstable() ? "Marriages not stable\n" : "Stable matchup\n");

return 0; }</lang>

Output:
Pairing:
   Abe - Ivy
   Bob - Cath
   Col - Dee
   Dan - Fay
    Ed - Jan
  Fred - Bea
   Gav - Gay
   Hal - Eve
   Ian - Hope
   Jon - Abi
Stable matchup

But if Bob and Fred were to swap:
    Fred (w/ Cath) and  Ivy (w/  Abe) prefer each other over current pairing.
     Bob (w/  Bea) and  Fay (w/  Dan) prefer each other over current pairing.
     Bob (w/  Bea) and Hope (w/  Ian) prefer each other over current pairing.
     Bob (w/  Bea) and  Abi (w/  Jon) prefer each other over current pairing.
    Fred (w/ Cath) and  Dee (w/  Col) prefer each other over current pairing.
    Fred (w/ Cath) and  Abi (w/  Jon) prefer each other over current pairing.
Marriages not stable

C++

<lang cpp>#include <algorithm>

  1. include <iostream>
  2. include <map>
  3. include <queue>
  4. include <string>
  5. include <vector>

using namespace std;

const char *men_data[][11] = {

   { "abe",  "abi","eve","cath","ivy","jan","dee","fay","bea","hope","gay" },
   { "bob",  "cath","hope","abi","dee","eve","fay","bea","jan","ivy","gay" },
   { "col",  "hope","eve","abi","dee","bea","fay","ivy","gay","cath","jan" },
   { "dan",  "ivy","fay","dee","gay","hope","eve","jan","bea","cath","abi" },
   { "ed",   "jan","dee","bea","cath","fay","eve","abi","ivy","hope","gay" },
   { "fred", "bea","abi","dee","gay","eve","ivy","cath","jan","hope","fay" },
   { "gav",  "gay","eve","ivy","bea","cath","abi","dee","hope","jan","fay" },
   { "hal",  "abi","eve","hope","fay","ivy","cath","jan","bea","gay","dee" },
   { "ian",  "hope","cath","dee","gay","bea","abi","fay","ivy","jan","eve" },
   { "jon",  "abi","fay","jan","gay","eve","bea","dee","cath","ivy","hope" }

};

const char *women_data[][11] = {

   { "abi",  "bob","fred","jon","gav","ian","abe","dan","ed","col","hal" },
   { "bea",  "bob","abe","col","fred","gav","dan","ian","ed","jon","hal" },
   { "cath", "fred","bob","ed","gav","hal","col","ian","abe","dan","jon" },
   { "dee",  "fred","jon","col","abe","ian","hal","gav","dan","bob","ed" },
   { "eve",  "jon","hal","fred","dan","abe","gav","col","ed","ian","bob" },
   { "fay",  "bob","abe","ed","ian","jon","dan","fred","gav","col","hal" },
   { "gay",  "jon","gav","hal","fred","bob","abe","col","ed","dan","ian" },
   { "hope", "gav","jon","bob","abe","ian","dan","hal","ed","col","fred" },
   { "ivy",  "ian","col","hal","gav","fred","bob","abe","ed","jon","dan" },
   { "jan",  "ed","hal","gav","abe","bob","jon","col","ian","fred","dan" }

};

typedef vector<string> PrefList; typedef map<string, PrefList> PrefMap; typedef map<string, string> Couples;

// Does 'first' appear before 'second' in preference list? bool prefers(const PrefList &prefer, const string &first, const string &second) {

   for (PrefList::const_iterator it = prefer.begin(); it != prefer.end(); ++it)
   {
       if (*it == first) return true;
       if (*it == second) return false;
   }
   return false; // no preference

}

void check_stability(const Couples &engaged, const PrefMap &men_pref, const PrefMap &women_pref) {

   cout << "Stablility:\n";
   bool stable = true;
   for (Couples::const_iterator it = engaged.begin(); it != engaged.end(); ++it)
   {
       const string &bride = it->first;
       const string &groom = it->second;
       const PrefList &preflist = men_pref.at(groom);
       for (PrefList::const_iterator it = preflist.begin(); it != preflist.end(); ++it)
       {
           if (*it == bride) // he prefers his bride
               break;
           if (prefers(preflist, *it, bride) && // he prefers another woman
               prefers(women_pref.at(*it), groom, engaged.at(*it))) // other woman prefers him
           {
               cout << "\t" << *it <<
                   " prefers " << groom <<
                   " over " << engaged.at(*it) <<
                   " and " << groom <<
                   " prefers " << *it <<
                   " over " << bride << "\n";
               stable = false;
           }
       }
   }
   if (stable) cout << "\t(all marriages stable)\n";

}

int main() {

   PrefMap men_pref, women_pref;
   queue<string> bachelors;
   // init data structures
   for (int i = 0; i < 10; ++i) // person
   {
       for (int j = 1; j < 11; ++j) // preference
       {
             men_pref[  men_data[i][0]].push_back(  men_data[i][j]);
           women_pref[women_data[i][0]].push_back(women_data[i][j]);
       }
       bachelors.push(men_data[i][0]);
   }
   Couples engaged; // <woman,man>
   cout << "Matchmaking:\n";
   while (!bachelors.empty())
   {
       const string &suitor = bachelors.front();
       const PrefList &preflist = men_pref[suitor];
       for (PrefList::const_iterator it = preflist.begin(); it != preflist.end(); ++it)
       {
           const string &bride = *it;
           if (engaged.find(bride) == engaged.end()) // she's available
           {
               cout << "\t" << bride << " and " << suitor << "\n";
               engaged[bride] = suitor; // hook up
               break;
           }
           const string &groom = engaged[bride];
           if (prefers(women_pref[bride], suitor, groom))
           {
               cout << "\t" << bride << " dumped " << groom << " for " << suitor << "\n";
               bachelors.push(groom); // dump that zero
               engaged[bride] = suitor; // get a hero
               break;
           }
       }
       bachelors.pop(); // pop at the end to not invalidate suitor reference
   }
   cout << "Engagements:\n";
   for (Couples::const_iterator it = engaged.begin(); it != engaged.end(); ++it)
   {
       cout << "\t" << it->first << " and " << it->second << "\n";
   }
   check_stability(engaged, men_pref, women_pref);
   cout << "Perturb:\n";
   std::swap(engaged["abi"], engaged["bea"]);
   cout << "\tengage abi with " << engaged["abi"] << " and bea with " << engaged["bea"] << "\n";
   check_stability(engaged, men_pref, women_pref);

}</lang>

Output:
Matchmaking:
	abi and abe
	cath and bob
	hope and col
	ivy and dan
	jan and ed
	bea and fred
	gay and gav
	eve and hal
	hope dumped col for ian
	abi dumped abe for jon
	dee and col
	ivy dumped dan for abe
	fay and dan
Engagements:
	abi and jon
	bea and fred
	cath and bob
	dee and col
	eve and hal
	fay and dan
	gay and gav
	hope and ian
	ivy and abe
	jan and ed
Stablility:
	(all marriages stable)
Perturb:
	engage abi with fred and bea with jon
Stablility:
	bea prefers fred over jon and fred prefers bea over abi
	fay prefers jon over dan and jon prefers fay over bea
	gay prefers jon over gav and jon prefers gay over bea
	eve prefers jon over hal and jon prefers eve over bea

C#

(This is a straight-up translation of the Objective-C version.) <lang csharp>using System; using System.Collections.Generic;

namespace StableMarriage {

   class Person
   {
       private int _candidateIndex;
       public string Name { get; set; }
       public List<Person> Prefs { get; set; }
       public Person Fiance { get; set; }
       
       public Person(string name) {
           Name = name;
           Prefs = null;
           Fiance = null;
           _candidateIndex = 0;
       }
       public bool Prefers(Person p) {
           return Prefs.FindIndex(o => o == p) < Prefs.FindIndex(o => o == Fiance);
       }
       public Person NextCandidateNotYetProposedTo() {
           if (_candidateIndex >= Prefs.Count) return null;
           return Prefs[_candidateIndex++];
       }
       public void EngageTo(Person p) {
           if (p.Fiance != null) p.Fiance.Fiance = null;
           p.Fiance = this;
           if (Fiance != null) Fiance.Fiance = null;
           Fiance = p;
       }
   }
   
   static class MainClass
   {
       static public bool IsStable(List<Person> men) {
           List<Person> women = men[0].Prefs;
           foreach (Person guy in men) {
               foreach (Person gal in women) {
                   if (guy.Prefers(gal) && gal.Prefers(guy))
                       return false;
               }
           }
           return true;
       }
       
       static void DoMarriage() {
           Person abe  = new Person("abe");
           Person bob  = new Person("bob");
           Person col  = new Person("col");
           Person dan  = new Person("dan");
           Person ed   = new Person("ed");
           Person fred = new Person("fred");
           Person gav  = new Person("gav");
           Person hal  = new Person("hal");
           Person ian  = new Person("ian");
           Person jon  = new Person("jon");
           Person abi  = new Person("abi");
           Person bea  = new Person("bea");
           Person cath = new Person("cath");
           Person dee  = new Person("dee");
           Person eve  = new Person("eve");
           Person fay  = new Person("fay");
           Person gay  = new Person("gay");
           Person hope = new Person("hope");
           Person ivy  = new Person("ivy");
           Person jan  = new Person("jan");
           
           abe.Prefs  = new List<Person>() {abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay};
           bob.Prefs  = new List<Person>() {cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay};
           col.Prefs  = new List<Person>() {hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan};
           dan.Prefs  = new List<Person>() {ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi};
           ed.Prefs   = new List<Person>() {jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay};
           fred.Prefs = new List<Person>() {bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay};
           gav.Prefs  = new List<Person>() {gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay};
           hal.Prefs  = new List<Person>() {abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee};
           ian.Prefs  = new List<Person>() {hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve};
           jon.Prefs  = new List<Person>() {abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope};
           abi.Prefs  = new List<Person>() {bob, fred, jon, gav, ian, abe, dan, ed, col, hal};
           bea.Prefs  = new List<Person>() {bob, abe, col, fred, gav, dan, ian, ed, jon, hal};
           cath.Prefs = new List<Person>() {fred, bob, ed, gav, hal, col, ian, abe, dan, jon};
           dee.Prefs  = new List<Person>() {fred, jon, col, abe, ian, hal, gav, dan, bob, ed};
           eve.Prefs  = new List<Person>() {jon, hal, fred, dan, abe, gav, col, ed, ian, bob};
           fay.Prefs  = new List<Person>() {bob, abe, ed, ian, jon, dan, fred, gav, col, hal};
           gay.Prefs  = new List<Person>() {jon, gav, hal, fred, bob, abe, col, ed, dan, ian};
           hope.Prefs = new List<Person>() {gav, jon, bob, abe, ian, dan, hal, ed, col, fred};
           ivy.Prefs  = new List<Person>() {ian, col, hal, gav, fred, bob, abe, ed, jon, dan};
           jan.Prefs  = new List<Person>() {ed, hal, gav, abe, bob, jon, col, ian, fred, dan};
           
           List<Person> men = new List<Person>(abi.Prefs);
           
           int freeMenCount = men.Count;
           while (freeMenCount > 0) {
               foreach (Person guy in men) {
                   if (guy.Fiance == null) {
                       Person gal = guy.NextCandidateNotYetProposedTo();
                       if (gal.Fiance == null) {
                           guy.EngageTo(gal);
                           freeMenCount--;
                       } else if (gal.Prefers(guy)) {
                           guy.EngageTo(gal);
                       }
                   }
               }
           }
           
           foreach (Person guy in men) {
               Console.WriteLine("{0} is engaged to {1}", guy.Name, guy.Fiance.Name);
           }
           Console.WriteLine("Stable = {0}", IsStable(men));
           
           Console.WriteLine("\nSwitching fred & jon's partners");
           Person jonsFiance = jon.Fiance;
           Person fredsFiance = fred.Fiance;
           fred.EngageTo(jonsFiance);
           jon.EngageTo(fredsFiance);
           Console.WriteLine("Stable = {0}", IsStable(men));
       }
       
       public static void Main(string[] args)
       {
           DoMarriage();
       }
   }

}</lang>

Output:
bob is engaged to cath
fred is engaged to bea
jon is engaged to abi
gav is engaged to gay
ian is engaged to hope
abe is engaged to ivy
dan is engaged to fay
ed is engaged to jan
col is engaged to dee
hal is engaged to eve
Stable = True

Switching fred & jon's partners
Stable = False

CoffeeScript

<lang coffeescript>class Person

 constructor: (@name, @preferences) ->
   @mate = null
   @best_mate_rank = 0
   @rank = {}
   for preference, i in @preferences
     @rank[preference] = i
 
 preferred_mate_name: =>
   @preferences[@best_mate_rank]
   
 reject: =>
   @best_mate_rank += 1
   
 set_mate: (mate) =>
   @mate = mate
 
 offer_mate: (free_mate, reject_mate_cb) =>  
   if @mate
     if @covets(free_mate)
       console.log "#{free_mate.name} steals #{@name} from #{@mate.name}"
       reject_mate_cb @mate
       free_mate.set_mate @
       @set_mate free_mate
     else
       console.log "#{free_mate.name} cannot steal #{@name} from #{@mate.name}"
       reject_mate_cb free_mate
   else
     console.log "#{free_mate.name} gets #{@name} first"
     free_mate.set_mate @
     @set_mate free_mate
     
 happiness: =>
   @rank[@mate.name]
   
 covets: (other_mate) =>
   @rank[other_mate.name] <= @rank[@mate.name]

persons_by_name = (persons) ->

 hsh = {}
 for person in persons
   hsh[person.name] = person
 hsh
    

mate_off = (guys, gals) ->

 free_pursuers = (guy for guy in guys)
 guys_by_name = persons_by_name guys
 gals_by_name = persons_by_name gals
 while free_pursuers.length > 0
   free_pursuer = free_pursuers.shift()
   gal_name = free_pursuer.preferred_mate_name()
   gal = gals_by_name[gal_name]
   reject_mate_cb = (guy) ->
     guy.reject()
     free_pursuers.push guy
   gal.offer_mate free_pursuer, reject_mate_cb


report_on_mates = (guys) ->

 console.log "\n----Marriage Report"
 for guy, i in guys
   throw Error("illegal marriage") if guy.mate.mate isnt guy
   console.log guy.name, guy.mate.name, \
     "(his choice #{guy.happiness()}, her choice #{guy.mate.happiness()} )"

report_potential_adulteries = (guys) ->

 for guy1, i in guys
   gal1 = guy1.mate
   for j in [0...i]
     guy2 = guys[j]
     gal2 = guy2.mate
     if guy1.covets(gal2) and gal2.covets(guy1)
       console.log "#{guy1.name} and #{gal2.name} would stray"
     if guy2.covets(gal1) and gal1.covets(guy2)
       console.log "#{guy2.name} and #{gal1.name} would stray"

perturb = (guys) ->

 # mess up marriages by swapping two couples...this is mainly to drive
 # out that report_potential_adulteries will actually work
 guy0 = guys[0]
 guy1 = guys[1]
 gal0 = guy0.mate
 gal1 = guy1.mate
 console.log "\nPerturbing with #{guy0.name}, #{gal0.name}, #{guy1.name}, #{gal1.name}"
 guy0.set_mate gal1
 guy1.set_mate gal0
 gal1.set_mate guy0
 gal0.set_mate guy1


Population = ->

 guy_preferences =
  abe:  ['abi', 'eve', 'cath', 'ivy', 'jan', 'dee', 'fay', 'bea', 'hope', 'gay']
  bob:  ['cath', 'hope', 'abi', 'dee', 'eve', 'fay', 'bea', 'jan', 'ivy', 'gay']
  col:  ['hope', 'eve', 'abi', 'dee', 'bea', 'fay', 'ivy', 'gay', 'cath', 'jan']
  dan:  ['ivy', 'fay', 'dee', 'gay', 'hope', 'eve', 'jan', 'bea', 'cath', 'abi']
  ed:   ['jan', 'dee', 'bea', 'cath', 'fay', 'eve', 'abi', 'ivy', 'hope', 'gay']
  fred: ['bea', 'abi', 'dee', 'gay', 'eve', 'ivy', 'cath', 'jan', 'hope', 'fay']
  gav:  ['gay', 'eve', 'ivy', 'bea', 'cath', 'abi', 'dee', 'hope', 'jan', 'fay']
  hal:  ['abi', 'eve', 'hope', 'fay', 'ivy', 'cath', 'jan', 'bea', 'gay', 'dee']
  ian:  ['hope', 'cath', 'dee', 'gay', 'bea', 'abi', 'fay', 'ivy', 'jan', 'eve']
  jon:  ['abi', 'fay', 'jan', 'gay', 'eve', 'bea', 'dee', 'cath', 'ivy', 'hope']

 gal_preferences =
  abi:  ['bob', 'fred', 'jon', 'gav', 'ian', 'abe', 'dan', 'ed', 'col', 'hal']
  bea:  ['bob', 'abe', 'col', 'fred', 'gav', 'dan', 'ian', 'ed', 'jon', 'hal']
  cath: ['fred', 'bob', 'ed', 'gav', 'hal', 'col', 'ian', 'abe', 'dan', 'jon']
  dee:  ['fred', 'jon', 'col', 'abe', 'ian', 'hal', 'gav', 'dan', 'bob', 'ed']
  eve:  ['jon', 'hal', 'fred', 'dan', 'abe', 'gav', 'col', 'ed', 'ian', 'bob']
  fay:  ['bob', 'abe', 'ed', 'ian', 'jon', 'dan', 'fred', 'gav', 'col', 'hal']
  gay:  ['jon', 'gav', 'hal', 'fred', 'bob', 'abe', 'col', 'ed', 'dan', 'ian']
  hope: ['gav', 'jon', 'bob', 'abe', 'ian', 'dan', 'hal', 'ed', 'col', 'fred']
  ivy:  ['ian', 'col', 'hal', 'gav', 'fred', 'bob', 'abe', 'ed', 'jon', 'dan']
  jan:  ['ed', 'hal', 'gav', 'abe', 'bob', 'jon', 'col', 'ian', 'fred', 'dan']
 guys = (new Person(name, preferences) for name, preferences of guy_preferences)
 gals = (new Person(name, preferences) for name, preferences of gal_preferences)
 [guys, gals]

do ->

 [guys, gals] = Population()
 mate_off guys, gals
 report_on_mates guys
 report_potential_adulteries guys
 perturb guys
 report_on_mates guys
 report_potential_adulteries guys</lang>
Output:
> coffee stable_marriage.coffee 
abe gets abi first
bob gets cath first
col gets hope first
dan gets ivy first
ed gets jan first
fred gets bea first
gav gets gay first
hal cannot steal abi from abe
ian steals hope from col
jon steals abi from abe
hal gets eve first
col cannot steal eve from hal
abe cannot steal eve from hal
col cannot steal abi from jon
abe cannot steal cath from bob
col gets dee first
abe steals ivy from dan
dan gets fay first

----Marriage Report
abe ivy (his choice 3, her choice 6 )
bob cath (his choice 0, her choice 1 )
col dee (his choice 3, her choice 2 )
dan fay (his choice 1, her choice 5 )
ed jan (his choice 0, her choice 0 )
fred bea (his choice 0, her choice 3 )
gav gay (his choice 0, her choice 1 )
hal eve (his choice 1, her choice 1 )
ian hope (his choice 0, her choice 4 )
jon abi (his choice 0, her choice 2 )

Perturbing with abe, ivy, bob, cath

----Marriage Report
abe cath (his choice 2, her choice 7 )
bob ivy (his choice 8, her choice 5 )
col dee (his choice 3, her choice 2 )
dan fay (his choice 1, her choice 5 )
ed jan (his choice 0, her choice 0 )
fred bea (his choice 0, her choice 3 )
gav gay (his choice 0, her choice 1 )
hal eve (his choice 1, her choice 1 )
ian hope (his choice 0, her choice 4 )
jon abi (his choice 0, her choice 2 )
bob and cath would stray
bob and fay would stray
bob and bea would stray
bob and hope would stray
bob and abi would stray

ColdFusion

<lang cfm> PERSON.CFC

component displayName="Person" accessors="true" {

   property name="Name" type="string";
   property name="MrOrMrsGoodEnough" type="Person";
   property name="UnrealisticExpectations" type="array";
   property name="PersonalHistory" type="array";
   public Person function init( required String name ) {
       setName( arguments.name );
       setPersonalHistory([ getName() & " is on the market." ]);
       this.HotnessScale = 0;
       return this;
   }
   public Boolean function hasSettled() {
       // if we have settled, return true;
       return isInstanceOf( getMrOrMrsGoodEnough(), "Person" );
   }
   public Person function getBestOfWhatIsLeft() {
       // increment the hotness scale...1 is best, 10 is...well...VERY settling.
       this.HotnessScale++;
       // get the match from the current rung in the barrel
       var bestChoice = getUnrealisticExpectations()[ this.HotnessScale ];
       return bestChoice;
   }
   public Boolean function wouldRatherBeWith( required Person person ) {
       // only compare if we've already settled on a potential mate
       if( isInstanceOf( this.getMrOrMrsGoodEnough(), "Person" ) ) {
           // if the new person's hotness is greater (numerically smaller) than our current beau...
           return getHotness( this, arguments.person ) < getHotness( this, this.getMrOrMrsGoodEnough() );
       }
       return false; 
   }
   public Void function settle( required Person person ) {
       if( person.hasSettled() ) {
           // this is the match we want. Force a break up of a previous relationship (sorry!)
           dumpLikeATonOfBricks( person );
       }
       person.setMrOrMrsGoodEnough( this );
       if( hasSettled() ) {
           // this is the match we want, so write a dear john to our current match
           dumpLikeATonOfBricks( this );
       }
       logHookup( arguments.person );
       // we've found the mate of our dreams!
       setMrOrMrsGoodEnough( arguments.person );
   }
   public Void function swing( required Person person ) {
       // get our spouses
       var mySpouse = getMrOrMrsGoodEnough();
       var notMySpouse = arguments.person.getMrOrMrsGoodEnough();
       // swap em'
       setMrOrMrsGoodEnough( notMySpouse );
       person.setMrOrMrsGoodEnough( mySpouse );
   }
   public Void function dumpLikeATonOfBricks( required Person person ) {
       logBreakup( arguments.person );
       person.getMrOrMrsGoodEnough().setMrOrMrsGoodEnough( JavaCast( "null", "" ) );
   }
   public String function psychoAnalyze() {
       logNuptuals();
       logRegrets();
       var personalJourney = "";
       for( var entry in getPersonalHistory() ) {
           personalJourney = personalJourney & entry & "
"; } return personalJourney; }
   private Numeric function getHotness( required Person pursuer, required Person pursued ) {
       var pursuersExpectations = pursuer.getUnrealisticExpectations();
       var hotnessFactor = 1;
       for( var hotnessFactor=1; hotnessFactor<=arrayLen( pursuersExpectations ); hotnessFactor++ ) {
           if( pursuersExpectations[ hotnessFactor ].getName()==arguments.pursued.getName() ) {
               return hotnessFactor;
           }
       }
   }
   private Void function logRegrets() {
       var spouse = getMrOrMrsGoodEnough();
       var spouseHotness = getHotness( this, spouse );
       var myHotness = getHotness( spouse, this );
       if( spouseHotness == 1 && myHotness == 1 ) {
           arrayAppend( getPersonalHistory(), "Yes, yes, the beautiful people always find happy endings: #getName()# (her ###myHotness#), #spouse.getName()# (his ###spouseHotness#)");
       }
       else if( spouseHotness == myHotness ) {
           arrayAppend( getPersonalHistory(), "#getName()# (her ###myHotness#) was made for #spouse.getName()# (his ###spouseHotness#). How precious.");
       }
       else if( spouseHotness > myHotness ) {
           arrayAppend( getPersonalHistory(), "#getName()# (her ###myHotness#) could have done better than #spouse.getName()# (his ###spouseHotness#). Poor slob.");
       }
       else {
           arrayAppend( getPersonalHistory(), "#getName()# (her ###myHotness#) is a lucky bastard to have landed #spouse.getName()# (his ###spouseHotness#).");
       }
   }
   private Void function logNuptuals() {
       arrayAppend( getPersonalHistory(), "#getName()# has settled for #getMrOrMrsGoodEnough().getName()#." );
   }
   private Void function logHookup( required Person person ) {
       var winnerHotness = getHotness( this, arguments.person );
       var myHotness = getHotness( arguments.person, this );
       arrayAppend( getPersonalHistory(), "#getName()# (her ###myHotness#) is checking out #arguments.person.getName()# (his ###winnerHotness#), but wants to keep his options open.");
   }
   private Void function logBreakup( required Person person ) {
       var scrub = person.getMrOrMrsGoodEnough();
       var scrubHotness = getHotness( person, scrub );
       var myHotness = getHotness( person, this );
       arrayAppend( getPersonalHistory(), "#getName()# is so hot (her ###myHotness#) that #person.getName()# is dumping #scrub.getName()# (her ###scrubHotness#)");
   }

} </lang> <lang cfm> INDEX.CFM

<cfscript>

   /**
    * Let's get these crazy kids married!
    * @men.hint The men who want to get married
    */
   function doCreepyMassMarriages( required Array men ) {
       marriagesAreStable = false;
       while( !marriagesAreStable ) {
           marriagesAreStable = true;
           for( man in men ) {
               if( !man.hasSettled() ) {
                   marriagesAreStable = false;
                   sexyLady = man.getBestOfWhatIsLeft();
                   if( !sexyLady.hasSettled() || sexyLady.wouldRatherBeWith( man ) ) {
                       man.settle( sexyLady );
                   }
               }
           }
       }
       return men;
   }
   /**
    * We played God...now let's see if society is going to survive
    * @men.hint The married men
    * @women.hint The married women
    */
   function isSocietyStable( required Array men, required Array women ) {
       // loop over married men
       for( var man in arguments.men ) {
           // loop over married women
           for( var woman in arguments.women ) {
               // if the man does not prefer this woman to his current spouse, and the women
               // doesn't prefer the man to her current spouse, this is the best possible match
               if( man.wouldRatherBeWith( woman ) && woman.wouldRatherBeWith( man ) ) {
                   return false;
               }
           }
       }
       return true;
   }
   // the men
   abe = new Person( "Abe" );
   bob = new Person( "Bob" );
   col = new Person( "Col" );
   dan = new Person( "Dan" );
   ed = new Person( "Ed" );
   fred = new Person( "Fred" );
   gav = new Person( "Gav" );
   hal = new Person( "Hal" );
   ian = new Person( "Ian" );
   jon = new Person( "Jon" );
   men = [ abe, bob, col, dan, ed, fred, gav, hal, ian, jon ];
   // the women
   abi = new Person( "Abi" );
   bea = new Person( "Bea" );
   cath = new Person( "Cath" );
   dee = new Person( "Dee" );
   eve = new Person( "Eve" );
   fay = new Person( "Fay" );
   gay = new Person( "Gay" );
   hope = new Person( "Hope" );
   ivy = new Person( "Ivy" );
   jan = new Person( "Jan" );
   women = [ abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan ];
   // set unrealistic expectations for the men
   abe.setUnrealisticExpectations([ abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay ]);
   bob.setUnrealisticExpectations([ cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay ]);
   col.setUnrealisticExpectations([ hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan ]);
   dan.setUnrealisticExpectations([ ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi ]);
   ed.setUnrealisticExpectations([ jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay ]);
   fred.setUnrealisticExpectations([ bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay ]);
   gav.setUnrealisticExpectations([ gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay ]);
   hal.setUnrealisticExpectations([ abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee ]);
   ian.setUnrealisticExpectations([ hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve ]);
   jon.setUnrealisticExpectations([ abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope ]);
   // set unrealistic expectations for the women
   abi.setUnrealisticExpectations([ bob, fred, jon, gav, ian, abe, dan, ed, col, hal ]);
   bea.setUnrealisticExpectations([ bob, abe, col, fred, gav, dan, ian, ed, jon, hal ]);
   cath.setUnrealisticExpectations([ fred, bob, ed, gav, hal, col, ian, abe, dan, jon ]);
   dee.setUnrealisticExpectations([ fred, jon, col, abe, ian, hal, gav, dan, bob, ed ]);
   eve.setUnrealisticExpectations([ jon, hal, fred, dan, abe, gav, col, ed, ian, bob ]);
   fay.setUnrealisticExpectations([ bob, abe, ed, ian, jon, dan, fred, gav, col, hal ]);
   gay.setUnrealisticExpectations([ jon, gav, hal, fred, bob, abe, col, ed, dan, ian ]);
   hope.setUnrealisticExpectations([ gav, jon, bob, abe, ian, dan, hal, ed, col, fred ]);
   ivy.setUnrealisticExpectations([ ian, col, hal, gav, fred, bob, abe, ed, jon, dan ]);
   jan.setUnrealisticExpectations([ ed, hal, gav, abe, bob, jon, col, ian, fred, dan ]);
   // here comes the bride, duhn, duhn, duh-duhn
   possiblyHappilyMarriedMen = doCreepyMassMarriages( men );
   // let's see who shacked up!
   for( man in possiblyHappilyMarriedMen ) {
       writeoutput( man.psychoAnalyze() & "
" ); } // check if society is stable if( isSocietyStable( men, women ) ) { writeoutput( "Hey, look at that. Creepy social engineering works. Sort of...

" ); } // what happens if couples start swingin'? jon.swing( fred ); writeoutput( "Swapping Jon and Fred's wives...will society survive?

" ); // check if society is still stable after the swingers if( !isSocietyStable( men, women ) ) { writeoutput( "Nope, now everything is broken. Sharing spouses doesn't work, kids.
" ); }

</cfscript> </lang>

Output:
Abe is on the market.
Abe (her #6) is checking out Abi (his #1), but wants to keep his options open.
Abe (her #5) is checking out Eve (his #2), but wants to keep his options open.
Abe is so hot (her #7) that Ivy is dumping Dan (her #10)
Abe (her #7) is checking out Ivy (his #4), but wants to keep his options open.
Abe has settled for Ivy.
Abe (her #7) is lucky to have landed Ivy (his #4).

Bob is on the market.
Bob (her #2) is checking out Cath (his #1), but wants to keep his options open.
Bob has settled for Cath.
Bob (her #2) is lucky to have landed Cath (his #1).

Col is on the market.
Col (her #9) is checking out Hope (his #1), but wants to keep his options open.
Col (her #3) is checking out Dee (his #4), but wants to keep his options open.
Col has settled for Dee.
Col (her #3) could have done better than Dee (his #4).

Dan is on the market.
Dan (her #10) is checking out Ivy (his #1), but wants to keep his options open.
Dan (her #6) is checking out Fay (his #2), but wants to keep his options open.
Dan has settled for Fay.
Dan (her #6) is lucky to have landed Fay (his #2).

Ed is on the market.
Ed (her #1) is checking out Jan (his #1), but wants to keep his options open.
Ed has settled for Jan.
Yes, yes, the beautiful people always find happy endings: Ed (her #1), Jan (his #1)

Fred is on the market.
Fred (her #4) is checking out Bea (his #1), but wants to keep his options open.
Fred has settled for Bea.
Fred (her #4) is lucky to have landed Bea (his #1).

Gav is on the market.
Gav (her #2) is checking out Gay (his #1), but wants to keep his options open.
Gav has settled for Gay.
Gav (her #2) is lucky to have landed Gay (his #1).

Hal is on the market.
Hal is so hot (her #2) that Eve is dumping Abe (her #5)
Hal (her #2) is checking out Eve (his #2), but wants to keep his options open.
Hal has settled for Eve.
Hal (her #2) was made for Eve (his #2). How precious.

Ian is on the market.
Ian is so hot (her #5) that Hope is dumping Col (her #9)
Ian (her #5) is checking out Hope (his #1), but wants to keep his options open.
Ian has settled for Hope.
Ian (her #5) is lucky to have landed Hope (his #1).

Jon is on the market.
Jon is so hot (her #3) that Abi is dumping Abe (her #6)
Jon (her #3) is checking out Abi (his #1), but wants to keep his options open.
Jon has settled for Abi.
Jon (her #3) is lucky to have landed Abi (his #1).
// Is society stable?
Hey, look at that. Creepy social engineering works. Sort of...

Swapping Jon and Fred's wives...will society survive?
// How about now? Still stable?
Nope, now everything is broken. Sharing spouses doesn't work, kids.

D

From the Python and Java versions: <lang d>import std.stdio, std.array, std.algorithm, std.string;


string[string] matchmaker(string[][string] guyPrefers,

                         string[][string] girlPrefers) /*@safe*/ {
   string[string] engagedTo;
   string[] freeGuys = guyPrefers.keys;
   while (freeGuys.length) {
       const string thisGuy = freeGuys[0];
       freeGuys.popFront();
       const auto thisGuyPrefers = guyPrefers[thisGuy];
       foreach (girl; thisGuyPrefers) {
           if (girl !in engagedTo) { // girl is free
               engagedTo[girl] = thisGuy;
               break;
           } else {
               string otherGuy = engagedTo[girl];
               string[] thisGirlPrefers = girlPrefers[girl];
               if (thisGirlPrefers.countUntil(thisGuy) <
                   thisGirlPrefers.countUntil(otherGuy)) {
                   // this girl prefers this guy to
                   // the guy she's engagedTo to.
                   engagedTo[girl] = thisGuy;
                   freeGuys ~= otherGuy;
                   break;
               }
               // else no change, keep looking for this guy
           }
       }
   }
   return engagedTo;

}


bool check(bool doPrint=false)(string[string] engagedTo,

                              string[][string] guyPrefers,
                              string[][string] galPrefers) @safe {
   enum MSG = "%s likes %s better than %s and %s " ~
              "likes %s better than their current partner";
   string[string] inverseEngaged;
   foreach (k, v; engagedTo)
       inverseEngaged[v] = k;
   foreach (she, he; engagedTo) {
       auto sheLikes = galPrefers[she];
       auto sheLikesBetter = sheLikes[0 .. sheLikes.countUntil(he)];
       auto heLikes = guyPrefers[he];
       auto heLikesBetter = heLikes[0 .. heLikes.countUntil(she)];
       foreach (guy; sheLikesBetter) {
           auto guysGirl = inverseEngaged[guy];
           auto guyLikes = guyPrefers[guy];
           if (guyLikes.countUntil(guysGirl) >
               guyLikes.countUntil(she)) {
               static if (doPrint)
                   writefln(MSG, she, guy, he, guy, she);
               return false;
           }
       }
       foreach (gal; heLikesBetter) {
           auto girlsGuy = engagedTo[gal];
           auto galLikes = galPrefers[gal];
           if (galLikes.countUntil(girlsGuy) >
               galLikes.countUntil(he)) {
               static if (doPrint)
                   writefln(MSG, he, gal, she, gal, he);
               return false;
           }
       }
   }
   return true;

}


void main() /*@safe*/ {

   auto guyData = "abe  abi eve cath ivy jan dee fay bea hope gay
                   bob  cath hope abi dee eve fay bea jan ivy gay
                   col  hope eve abi dee bea fay ivy gay cath jan
                   dan  ivy fay dee gay hope eve jan bea cath abi
                   ed   jan dee bea cath fay eve abi ivy hope gay
                   fred bea abi dee gay eve ivy cath jan hope fay
                   gav  gay eve ivy bea cath abi dee hope jan fay
                   hal  abi eve hope fay ivy cath jan bea gay dee
                   ian  hope cath dee gay bea abi fay ivy jan eve
                   jon  abi fay jan gay eve bea dee cath ivy hope";
   auto galData = "abi  bob fred jon gav ian abe dan ed col hal
                   bea  bob abe col fred gav dan ian ed jon hal
                   cath fred bob ed gav hal col ian abe dan jon
                   dee  fred jon col abe ian hal gav dan bob ed
                   eve  jon hal fred dan abe gav col ed ian bob
                   fay  bob abe ed ian jon dan fred gav col hal
                   gay  jon gav hal fred bob abe col ed dan ian
                   hope gav jon bob abe ian dan hal ed col fred
                   ivy  ian col hal gav fred bob abe ed jon dan
                   jan  ed hal gav abe bob jon col ian fred dan";
   string[][string] guyPrefers, galPrefers;
   foreach (line; guyData.splitLines())
       guyPrefers[split(line)[0]] = split(line)[1..$];
   foreach (line; galData.splitLines())
       galPrefers[split(line)[0]] = split(line)[1..$];
   writeln("Engagements:");
   auto engagedTo = matchmaker(guyPrefers, galPrefers);
   writeln("\nCouples:");
   string[] parts;
   foreach (k; engagedTo.keys.sort())
       writefln("%s is engagedTo to %s", k, engagedTo[k]);
   writeln();
   bool c = check!(true)(engagedTo, guyPrefers, galPrefers);
   writeln("Marriages are ", c ? "stable" : "unstable");
   writeln("\n\nSwapping two fiances to introduce an error");
   auto gals = galPrefers.keys.sort();
   swap(engagedTo[gals[0]], engagedTo[gals[1]]);
   foreach (gal; gals[0 .. 2])
       writefln("  %s is now engagedTo to %s", gal, engagedTo[gal]);
   writeln();
   c = check!(true)(engagedTo, guyPrefers, galPrefers);
   writeln("Marriages are ", c ? "stable" : "unstable");

}</lang>

Output:
Engagements:

Couples:
abi is engagedTo to jon
bea is engagedTo to fred
cath is engagedTo to bob
dee is engagedTo to col
eve is engagedTo to hal
fay is engagedTo to dan
gay is engagedTo to gav
hope is engagedTo to ian
ivy is engagedTo to abe
jan is engagedTo to ed

Marriages are stable


Swapping two fiances to introduce an error
  abi is now engagedTo to fred
  bea is now engagedTo to jon

fred likes bea better than abi and bea likes fred better than their current partner
Marriages are unstable

Stronger Version

<lang d>import std.stdio, std.algorithm, std.array;

enum F { abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan } enum M { abe, bob, col, dan, ed, fred, gav, hal, ian, jon }

alias PrefMapF = M[][F]; alias PrefMapM = F[][M]; alias Couples = M[F];

immutable PrefMapF womenPref; immutable PrefMapM menPref;

static this() pure nothrow @safe {

   with (F) with (M) {
       womenPref = [
            abi:  [bob, fred, jon, gav, ian, abe, dan, ed, col, hal],
            bea:  [bob, abe, col, fred, gav, dan, ian, ed, jon, hal],
            cath: [fred, bob, ed, gav, hal, col, ian, abe, dan, jon],
            dee:  [fred, jon, col, abe, ian, hal, gav, dan, bob, ed],
            eve:  [jon, hal, fred, dan, abe, gav, col, ed, ian, bob],
            fay:  [bob, abe, ed, ian, jon, dan, fred, gav, col, hal],
            gay:  [jon, gav, hal, fred, bob, abe, col, ed, dan, ian],
            hope: [gav, jon, bob, abe, ian, dan, hal, ed, col, fred],
            ivy:  [ian, col, hal, gav, fred, bob, abe, ed, jon, dan],
            jan:  [ed, hal, gav, abe, bob, jon, col, ian, fred, dan]
       ];
       menPref = [
            abe:  [abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay],
            bob:  [cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay],
            col:  [hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan],
            dan:  [ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi],
            ed:   [jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay],
            fred: [bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay],
            gav:  [gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay],
            hal:  [abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee],
            ian:  [hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve],
            jon:  [abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope]
       ];
   }

}

/// Does 'first' appear before 'second' in preference list? bool prefers(T)(in T[] preference, in T first, in T second) pure nothrow @safe @nogc if (is(T == F) || is(T == M)) {

   //const found = preference.findAmong([first, second]);
   immutable T[2] two = [first, second];
   const found = preference.findAmong(two[]);
   return !(found.empty || found.front == second);

}

void checkStability(in Couples engaged, in PrefMapM menPref,

                   in PrefMapF womenPref) @safe {
   "Stablility:".writeln;
   bool stable = true;
   foreach (immutable bride, immutable groom; engaged) {
       const prefList = menPref[groom];
       foreach (immutable pr; prefList) {
           if (pr == bride) // He prefers his bride.
               break;
           if (prefers(prefList, pr, bride) &&
               // He prefers another woman.
               prefers(womenPref[pr], groom, engaged[pr])) {
               // Other woman prefers him.
               writeln("\t", pr, " prefers ", groom, " over ",
                       engaged[pr], " and ", groom, " prefers ",
                       pr, " over ", bride);
               stable = false;
           }
       }
   }
   if (stable)
       "\t(all marriages stable)".writeln;

}

void main() /*@safe*/ {

   auto bachelors = menPref.keys.sort().release;// No queue in Phobos.
   Couples engaged;
   "Matchmaking:".writeln;
   while (!bachelors.empty) {
       immutable suitor = bachelors[0];
       bachelors.popFront;
       immutable prefList = menPref[suitor];
       foreach (immutable bride; prefList) {
           if (bride !in engaged) { // She's available.
               writeln("\t", bride, " and ", suitor);
               engaged[bride] = suitor; // Hook up.
               break;
           }
           immutable groom = engaged[bride];
           if (prefers(womenPref[bride], suitor, groom)) {
               writeln("\t", bride, " dumped ", groom,
                       " for ", suitor);
               bachelors ~= groom; // Dump that zero.
               engaged[bride] = suitor; // Get a hero.
               break;
           }
       }
   }
   "Engagements:".writeln;
   foreach (immutable first, immutable second; engaged)
       writeln("\t", first, " and ", second);
   checkStability(engaged, menPref, womenPref);
   "Perturb:".writeln;
   engaged[F.abi].swap(engaged[F.bea]);
   writeln("\tengage abi with ", engaged[F.abi],
           " and bea with ", engaged[F.bea]);
   checkStability(engaged, menPref, womenPref);

} </lang>

Output:
Matchmaking:
    abi and abe
    cath and bob
    hope and col
    ivy and dan
    jan and ed
    bea and fred
    gay and gav
    eve and hal
    hope dumped col for ian
    abi dumped abe for jon
    dee and col
    ivy dumped dan for abe
    fay and dan
Engagements:
    abi and jon
    ivy and abe
    eve and hal
    jan and ed
    bea and fred
    fay and dan
    cath and bob
    gay and gav
    hope and ian
    dee and col
Stablility:
    (all marriages stable)
Perturb:
    engage abi with fred and bea with jon
Stablility:
    bea prefers fred over jon and fred prefers bea over abi
    fay prefers jon over dan and jon prefers fay over bea
    gay prefers jon over gav and jon prefers gay over bea
    eve prefers jon over hal and jon prefers eve over bea

EchoLisp

<lang scheme> (lib 'hash)

input data

(define M-RANKS '(( abe abi eve cath ivy jan dee fay bea hope gay) ( bob cath hope abi dee eve fay bea jan ivy gay) ( col hope eve abi dee bea fay ivy gay cath jan) ( dan ivy fay dee gay hope eve jan bea cath abi) ( ed jan dee bea cath fay eve abi ivy hope gay) ( fred bea abi dee gay eve ivy cath jan hope fay) ( gav gay eve ivy bea cath abi dee hope jan fay) ( hal abi eve hope fay ivy cath jan bea gay dee) ( ian hope cath dee gay bea abi fay ivy jan eve) ( jon abi fay jan gay eve bea dee cath ivy hope)))

(define W-RANKS '(( abi bob fred jon gav ian abe dan ed col hal) ( bea bob abe col fred gav dan ian ed jon hal) ( cath fred bob ed gav hal col ian abe dan jon) ( dee fred jon col abe ian hal gav dan bob ed) ( eve jon hal fred dan abe gav col ed ian bob) ( fay bob abe ed ian jon dan fred gav col hal) ( gay jon gav hal fred bob abe col ed dan ian) ( hope gav jon bob abe ian dan hal ed col fred) ( ivy ian col hal gav fred bob abe ed jon dan) ( jan ed hal gav abe bob jon col ian fred dan)))

build preferences hash

(define (set-prefs ranks prefs)

   (for/list ((r ranks))
       (hash-set prefs (first r) (rest r))
       (first r)))
       

(define (engage m w) (hash-set ENGAGED m w) (hash-set ENGAGED w m) (writeln m w '👫 )) (define (disengage m w) (hash-remove! ENGAGED m ) (hash-remove! ENGAGED w) (writeln '💔 m w)) (define (engaged x) (hash-ref ENGAGED x)) (define (free? x) (not (engaged x))) (define (free-man men) (for ((man men)) #:break (free? man) => man #f))


(define (prefers? prefs x a b) (member b (member a (hash-ref prefs x))))

get first choice and remove it from prefs list

(define (first-choice prefs m)

   (define w (first (hash-ref prefs m)))
   (hash-set prefs m (rest (hash-ref prefs m)))
   w)
   
sets ENGAGED couples
https//en.wikipedia.org/wiki/Stable_marriage_problem

(define (stableMatching (prefs (make-hash)) (m) (w)) (define-global 'ENGAGED (make-hash))

 (define men   (set-prefs  M-RANKS prefs))
 (define women (set-prefs  W-RANKS prefs))
   (while (setv! m (free-man men))
       (set! w (first-choice prefs m))
       (if (free? w)
           (engage m w)
           (let [(dumped (engaged w))]
           (when (prefers? prefs w m dumped)
               (disengage w dumped)
               (engage w m)))))
(hash->list ENGAGED))
               
input
ENGAGED couples

(define (checkStable (prefs (make-hash)))

 (define men   (set-prefs  M-RANKS  prefs))
 (define women (set-prefs  W-RANKS  prefs))

(for* [(man men) (woman women)] #:continue (equal? woman (engaged man)) (when (and (prefers? prefs man woman (engaged man)) (prefers? prefs woman man (engaged woman))) (error 'not-stable (list man woman)))))

</lang>

Output:
(stableMatching)
👫     abe     abi    
👫     bob     cath    
👫     col     hope    
👫     dan     ivy    
👫     ed     jan    
👫     fred     bea    
👫     gav     gay    
👫     hal     eve    
💔     hope     col    
👫     hope     ian    
👫     col     dee    
💔     abi     abe    
👫     abi     jon    
💔     ivy     dan    
👫     ivy     abe    
👫     dan     fay    
  ((abe . ivy) (abi . jon) (bob . cath) (cath . bob) (col . dee) (hope . ian) (dan . fay) (ivy . abe) (ed . jan)
 (jan . ed) (fred . bea) (bea . fred) (gav . gay) (gay . gav) (hal . eve) (eve . hal) (ian . hope) (dee . col) (jon . abi) (fay . dan))

(disengage 'abe 'ivy)
(disengage 'hope 'ian)
(engage 'abe 'hope)
(engage 'ivy 'ian)
(checkStable)

💔     abe     ivy    
💔     hope     ian    
abe     hope     👫    
ivy     ian     👫    
😡 error: not-stable (abe bea)

F#

<lang fsharp>let menPrefs =

 Map.ofList
           ["abe",  ["abi";"eve";"cath";"ivy";"jan";"dee";"fay";"bea";"hope";"gay"];
            "bob",  ["cath";"hope";"abi";"dee";"eve";"fay";"bea";"jan";"ivy";"gay"];
            "col",  ["hope";"eve";"abi";"dee";"bea";"fay";"ivy";"gay";"cath";"jan"];
            "dan",  ["ivy";"fay";"dee";"gay";"hope";"eve";"jan";"bea";"cath";"abi"];
            "ed",   ["jan";"dee";"bea";"cath";"fay";"eve";"abi";"ivy";"hope";"gay"];
            "fred", ["bea";"abi";"dee";"gay";"eve";"ivy";"cath";"jan";"hope";"fay"];
            "gav",  ["gay";"eve";"ivy";"bea";"cath";"abi";"dee";"hope";"jan";"fay"];
            "hal",  ["abi";"eve";"hope";"fay";"ivy";"cath";"jan";"bea";"gay";"dee"];
            "ian",  ["hope";"cath";"dee";"gay";"bea";"abi";"fay";"ivy";"jan";"eve"];
            "jon",  ["abi";"fay";"jan";"gay";"eve";"bea";"dee";"cath";"ivy";"hope"];
           ]

let womenPrefs =

  Map.ofList
             ["abi",  ["bob";"fred";"jon";"gav";"ian";"abe";"dan";"ed";"col";"hal"];
              "bea",  ["bob";"abe";"col";"fred";"gav";"dan";"ian";"ed";"jon";"hal"];
              "cath", ["fred";"bob";"ed";"gav";"hal";"col";"ian";"abe";"dan";"jon"];
              "dee",  ["fred";"jon";"col";"abe";"ian";"hal";"gav";"dan";"bob";"ed"];
              "eve",  ["jon";"hal";"fred";"dan";"abe";"gav";"col";"ed";"ian";"bob"];
              "fay",  ["bob";"abe";"ed";"ian";"jon";"dan";"fred";"gav";"col";"hal"];
              "gay",  ["jon";"gav";"hal";"fred";"bob";"abe";"col";"ed";"dan";"ian"];
              "hope", ["gav";"jon";"bob";"abe";"ian";"dan";"hal";"ed";"col";"fred"];
              "ivy",  ["ian";"col";"hal";"gav";"fred";"bob";"abe";"ed";"jon";"dan"];
              "jan",  ["ed";"hal";"gav";"abe";"bob";"jon";"col";"ian";"fred";"dan"];
             ]

let men = menPrefs |> Map.toList |> List.map fst |> List.sort let women = womenPrefs |> Map.toList |> List.map fst |> List.sort


type Configuration =

{
  proposed: Map<string,string list>; // man -> list of women
  wifeOf: Map<string, string>; // man -> woman
  husbandOf: Map<string, string>;  // woman -> man
}


// query functions

let isFreeMan config man = config.wifeOf.TryFind man = None

let isFreeWoman config woman = config.husbandOf.TryFind woman = None

let hasProposedTo config man woman =

 defaultArg (config.proposed.TryFind(man)) []
 |> List.exists ((=) woman)

// helper let negate f = fun x -> not (f x)

// returns those 'women' who 'man' has not proposed to before let notProposedBy config man women = List.filter (negate (hasProposedTo config man)) women

let prefers (prefs:Map<string,string list>) w m1 m2 =

 let order = prefs.[w]
 let m1i = List.findIndex ((=) m1) order
 let m2i = List.findIndex ((=) m2) order
 m1i < m2i

let womanPrefers = prefers womenPrefs let manPrefers = prefers menPrefs

// returns the women that m likes better than his current fiancée let preferredWomen config m =

 let w = config.wifeOf.[m]
 women
 |> List.filter (fun w' -> manPrefers m w' w)  // '

// whether there is a woman who m likes better than his current fiancée // and who also likes him better than her current fiancé let prefersAWomanWhoAlsoPrefersHim config m =

 preferredWomen config m
 |> List.exists (fun w -> womanPrefers w m config.husbandOf.[w])

let isStable config =

 not (List.exists (prefersAWomanWhoAlsoPrefersHim config) men)


// modifiers (return new configurations)

let engage config man woman =

 { config with wifeOf = config.wifeOf.Add(man, woman);
               husbandOf = config.husbandOf.Add(woman, man) }

let breakOff config man =

 let woman = config.wifeOf.[man]
 { config with wifeOf = config.wifeOf.Remove(man);
               husbandOf = config.husbandOf.Remove(woman) }

let propose config m w =

 // remember the proposition
 let proposedByM = defaultArg (config.proposed.TryFind m) []
 let proposed' = config.proposed.Add(m, w::proposedByM) // '
 let config = { config with proposed = proposed'}  // '
 // actually try to engage
 if isFreeWoman config w then engage config m w
 else
   let m' = config.husbandOf.[w] // '
   if womanPrefers w m m' then // '
     let config = breakOff config m' // '
     engage config m w
   else
     config

// do one step of the algorithm; returns None if no more steps are possible let step config : Configuration option =

 let freeMen = men |> List.filter (isFreeMan config)
 let menWhoCanPropose =
   freeMen |>
   List.filter (fun man -> (notProposedBy config man women) <> [] )
 match menWhoCanPropose with
 | [] -> None
 | m::_ -> let unproposedByM = menPrefs.[m] |> notProposedBy config m
           // w is automatically the highest ranked because menPrefs.[m] is the source
           let w = List.head unproposedByM
           Some( propose config m w )
             

let rec loop config =

 match step config with
 | None -> config
 | Some config' -> loop config' // '


// find solution and print it let solution = loop { proposed = Map.empty<string, string list>;

                     wifeOf = Map.empty<string, string>;
                     husbandOf = Map.empty<string, string> }

for woman, man in Map.toList solution.husbandOf do

 printfn "%s is engaged to %s" woman man

printfn "Solution is stable: %A" (isStable solution)


// create unstable configuration by perturbing the solution let perturbed =

 let gal0 = women.[0]
 let gal1 = women.[1]
 let guy0 = solution.husbandOf.[gal0]
 let guy1 = solution.husbandOf.[gal1]
 { solution with wifeOf = solution.wifeOf.Add( guy0, gal1 ).Add( guy1, gal0 );
                 husbandOf = solution.husbandOf.Add( gal0, guy1 ).Add( gal1, guy0 ) }

printfn "Perturbed is stable: %A" (isStable perturbed)</lang>

Output:
abi is engaged to jon
bea is engaged to fred
cath is engaged to bob
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to abe
jan is engaged to ed
Solution is stable: true
Perturbed is stable: false

Go

<lang go>package main

import "fmt"

// Asymetry in the algorithm suggests different data structures for the // map value types of the proposers and the recipients. Proposers go down // their list of preferences in order, and do not need random access. // Recipients on the other hand must compare their preferences to arbitrary // proposers. A slice is adequate for proposers, but a map allows direct // lookups for recipients and avoids looping code. type proposers map[string][]string

var mPref = proposers{

   "abe": []string{
       "abi", "eve", "cath", "ivy", "jan",
       "dee", "fay", "bea", "hope", "gay"},
   "bob": []string{
       "cath", "hope", "abi", "dee", "eve",
       "fay", "bea", "jan", "ivy", "gay"},
   "col": []string{
       "hope", "eve", "abi", "dee", "bea",
       "fay", "ivy", "gay", "cath", "jan"},
   "dan": []string{
       "ivy", "fay", "dee", "gay", "hope",
       "eve", "jan", "bea", "cath", "abi"},
   "ed": []string{
       "jan", "dee", "bea", "cath", "fay",
       "eve", "abi", "ivy", "hope", "gay"},
   "fred": []string{
       "bea", "abi", "dee", "gay", "eve",
       "ivy", "cath", "jan", "hope", "fay"},
   "gav": []string{
       "gay", "eve", "ivy", "bea", "cath",
       "abi", "dee", "hope", "jan", "fay"},
   "hal": []string{
       "abi", "eve", "hope", "fay", "ivy",
       "cath", "jan", "bea", "gay", "dee"},
   "ian": []string{
       "hope", "cath", "dee", "gay", "bea",
       "abi", "fay", "ivy", "jan", "eve"},
   "jon": []string{
       "abi", "fay", "jan", "gay", "eve",
       "bea", "dee", "cath", "ivy", "hope"},

}

type recipients map[string]map[string]int

var wPref = recipients{

   "abi": map[string]int{
       "bob": 1, "fred": 2, "jon": 3, "gav": 4, "ian": 5,
       "abe": 6, "dan": 7, "ed": 8, "col": 9, "hal": 10},
   "bea": map[string]int{
       "bob": 1, "abe": 2, "col": 3, "fred": 4, "gav": 5,
       "dan": 6, "ian": 7, "ed": 8, "jon": 9, "hal": 10},
   "cath": map[string]int{
       "fred": 1, "bob": 2, "ed": 3, "gav": 4, "hal": 5,
       "col": 6, "ian": 7, "abe": 8, "dan": 9, "jon": 10},
   "dee": map[string]int{
       "fred": 1, "jon": 2, "col": 3, "abe": 4, "ian": 5,
       "hal": 6, "gav": 7, "dan": 8, "bob": 9, "ed": 10},
   "eve": map[string]int{
       "jon": 1, "hal": 2, "fred": 3, "dan": 4, "abe": 5,
       "gav": 6, "col": 7, "ed": 8, "ian": 9, "bob": 10},
   "fay": map[string]int{
       "bob": 1, "abe": 2, "ed": 3, "ian": 4, "jon": 5,
       "dan": 6, "fred": 7, "gav": 8, "col": 9, "hal": 10},
   "gay": map[string]int{
       "jon": 1, "gav": 2, "hal": 3, "fred": 4, "bob": 5,
       "abe": 6, "col": 7, "ed": 8, "dan": 9, "ian": 10},
   "hope": map[string]int{
       "gav": 1, "jon": 2, "bob": 3, "abe": 4, "ian": 5,
       "dan": 6, "hal": 7, "ed": 8, "col": 9, "fred": 10},
   "ivy": map[string]int{
       "ian": 1, "col": 2, "hal": 3, "gav": 4, "fred": 5,
       "bob": 6, "abe": 7, "ed": 8, "jon": 9, "dan": 10},
   "jan": map[string]int{
       "ed": 1, "hal": 2, "gav": 3, "abe": 4, "bob": 5,
       "jon": 6, "col": 7, "ian": 8, "fred": 9, "dan": 10},

}

func main() {

   // get parings by Gale/Shapley algorithm
   ps := pair(mPref, wPref)
   // show results
   fmt.Println("\nresult:")
   if !validateStable(ps, mPref, wPref) {
       return 
   }
   // perturb
   for {
       i := 0 
       var w2, m2 [2]string
       for w, m := range ps {
           w2[i] = w
           m2[i] = m
           if i == 1 {
               break
           }
           i++
       }
       fmt.Println("\nexchanging partners of", m2[0], "and", m2[1])
       ps[w2[0]] = m2[1]
       ps[w2[1]] = m2[0] 
       // validate perturbed parings
       if !validateStable(ps, mPref, wPref) {
           return
       }
       // if those happened to be stable as well, perturb more
   }

}

type parings map[string]string // map[recipient]proposer (or map[w]m)

// Pair implements the Gale/Shapley algorithm. func pair(pPref proposers, rPref recipients) parings {

   // code is destructive on the maps, so work with copies
   pFree := proposers{}
   for k, v := range pPref {
       pFree[k] = append([]string{}, v...)
   }
   rFree := recipients{}
   for k, v := range rPref {
       rFree[k] = v
   }
   // struct only used in this function.
   // preferences must be saved in case engagement is broken.
   type save struct {
       proposer string
       pPref    []string
       rPref    map[string]int
   }
   proposals := map[string]save{} // key is recipient (w)
   // WP pseudocode comments prefaced with WP: m is proposer, w is recipient.
   // WP: while ∃ free man m who still has a woman w to propose to
   for len(pFree) > 0 { // while there is a free proposer,
       var proposer string
       var ppref []string
       for proposer, ppref = range pFree {
           break // pick a proposer at random, whatever range delivers first.
       }
       if len(ppref) == 0 {
           continue // if proposer has no possible recipients, skip
       }
       // WP: w = m's highest ranked such woman to whom he has not yet proposed
       recipient := ppref[0] // highest ranged is first in list.
       ppref = ppref[1:]     // pop from list
       var rpref map[string]int
       var ok bool
       // WP: if w is free
       if rpref, ok = rFree[recipient]; ok {
           // WP: (m, w) become engaged
           // (common code follows if statement)
       } else {
           // WP: else some pair (m', w) already exists
           s := proposals[recipient] // get proposal saved preferences
           // WP: if w prefers m to m'
           if s.rPref[proposer] < s.rPref[s.proposer] {
               fmt.Println("engagement broken:", recipient, s.proposer)
               // WP: m' becomes free
               pFree[s.proposer] = s.pPref // return proposer to the map
               // WP: (m, w) become engaged
               rpref = s.rPref
               // (common code follows if statement)
           } else {
               // WP: else (m', w) remain engaged
               pFree[proposer] = ppref // update preferences in map
               continue
           } 
       }
       fmt.Println("engagement:", recipient, proposer)
       proposals[recipient] = save{proposer, ppref, rpref}
       delete(pFree, proposer)
       delete(rFree, recipient)
   }
   // construct return value 
   ps := parings{}
   for recipient, s := range proposals {
       ps[recipient] = s.proposer
   }
   return ps

}

func validateStable(ps parings, pPref proposers, rPref recipients) bool {

   for r, p := range ps {
       fmt.Println(r, p)
   }
   for r, p := range ps {
       for _, rp := range pPref[p] {
           if rp == r {
               break
           }
           rprefs := rPref[rp]
           if rprefs[p] < rprefs[ps[rp]] {
               fmt.Println("unstable.")
               fmt.Printf("%s and %s would prefer each other over"+
                   " their current pairings.\n", p, rp)
               return false
           }
       }
   }
   fmt.Println("stable.")
   return true

}</lang>

Output:
engagement: hope col
engagement: bea fred
engagement: ivy dan
engagement: cath bob
engagement: abi abe
engagement broken: abi abe
engagement: abi jon
engagement: gay gav
engagement: eve abe
engagement: jan ed
engagement broken: hope col
engagement: hope ian
engagement: dee col
engagement broken: eve abe
engagement: eve hal
engagement broken: ivy dan
engagement: ivy abe
engagement: fay dan

result:
fay dan
dee col
cath bob
hope ian
eve hal
jan ed
abi jon
gay gav
ivy abe
bea fred
stable.

exchanging partners of fred and dan
ivy abe
bea dan
fay fred
dee col
cath bob
hope ian
eve hal
jan ed
abi jon
gay gav
unstable.
dan and fay would prefer each other over their current pairings.

Groovy

Translation of: Java
(more or less) Uses explicit maps for preference ranking rather than list position. Uses Man and Woman enumerated types instead of string names, in order to take advantage of compile time type and constant checking to help keep the playas straight without a scorecard.

"Stable Matching" Solution: <lang groovy>import static Man.* import static Woman.*

Map<Woman,Man> match(Map<Man,Map<Woman,Integer>> guysGalRanking, Map<Woman,Map<Man,Integer>> galsGuyRanking) {

   Map<Woman,Man> engagedTo = new TreeMap()
   List<Man> freeGuys = (Man.values()).clone()
   while(freeGuys) {
       Man thisGuy = freeGuys[0]
       freeGuys -= thisGuy
       List<Woman> guyChoices = Woman.values().sort{ she -> - guysGalRanking[thisGuy][she] }
       for(Woman girl in guyChoices) {
           if(! engagedTo[girl]) {
               engagedTo[girl] = thisGuy
               break
           } else {
               Man thatGuy = engagedTo[girl]
               if (galsGuyRanking[girl][thisGuy] > galsGuyRanking[girl][thatGuy]) {
                   engagedTo[girl] = thisGuy
                   freeGuys << thatGuy
                   break
               }
           }
       }
   }
   engagedTo

}</lang>

"Stability Checking" Solution: (Could do more to eliminate common code. Maybe later.) <lang groovy>boolean isStable(Map<Woman,Man> matches, Map<Man,Map<Woman,Integer>> guysGalRanking, Map<Woman,Map<Man,Integer>> galsGuyRanking) {

   matches.collect{ girl, guy ->
       int guysRank = galsGuyRanking[girl][guy]
       List<Man> sheLikesBetter = Man.values().findAll{ he -> galsGuyRanking[girl][he] > guysRank }
       for(Man otherGuy : sheLikesBetter) {
           Woman otherGuyFiancee = matches.find{ pair -> pair.value == otherGuy }.key
           if(guysGalRanking[otherGuy][girl] > guysGalRanking[otherGuy][otherGuyFiancee]) {
               println """O. M. G. ... ${otherGuy} likes ${girl} better than ${otherGuyFiancee}, and ${girl} likes ${otherGuy} better than ${guy}!
                           I am TOTALLY 'shipping ${girl} and ${otherGuy} now!"""
               return false
           } 
       }
       
       int galsRank = guysGalRanking[guy][girl]
       List<Woman> heLikesBetter = Woman.values().findAll{ she -> guysGalRanking[guy][she] > galsRank }
       for(Woman otherGal : heLikesBetter) {
           Man otherGalFiance = matches[otherGal]
           if(galsGuyRanking[otherGal][guy] > galsGuyRanking[otherGal][otherGalFiance]) {
               println """O. M. G. ... ${otherGal} likes ${guy} better than ${otherGalFiance}, and ${guy} likes ${otherGal} better than ${girl}!
                           I am TOTALLY 'shipping ${guy} and ${otherGal} now!"""
               return false
           } 
       }
       true
   }.every()

}</lang>

Test (Stable and Perturbed): <lang groovy>enum Man {

   abe, bob, col, dan, ed, fred, gav, hal, ian, jon

}

enum Woman {

   abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan

}

Map<Man,Map<Woman,Integer>> mansWomanRanking = [

   (abe): [(abi):10, (eve):9, (cath):8, (ivy):7, (jan):6, (dee):5, (fay):4, (bea):3, (hope):2, (gay):1],
   (bob): [(cath):10, (hope):9, (abi):8, (dee):7, (eve):6, (fay):5, (bea):4, (jan):3, (ivy):2, (gay):1],
   (col): [(hope):10, (eve):9, (abi):8, (dee):7, (bea):6, (fay):5, (ivy):4, (gay):3, (cath):2, (jan):1],
   (dan): [(ivy):10, (fay):9, (dee):8, (gay):7, (hope):6, (eve):5, (jan):4, (bea):3, (cath):2, (abi):1],
   (ed):  [(jan):10, (dee):9, (bea):8, (cath):7, (fay):6, (eve):5, (abi):4, (ivy):3, (hope):2, (gay):1],
   (fred):[(bea):10, (abi):9, (dee):8, (gay):7, (eve):6, (ivy):5, (cath):4, (jan):3, (hope):2, (fay):1],
   (gav): [(gay):10, (eve):9, (ivy):8, (bea):7, (cath):6, (abi):5, (dee):4, (hope):3, (jan):2, (fay):1],
   (hal): [(abi):10, (eve):9, (hope):8, (fay):7, (ivy):6, (cath):5, (jan):4, (bea):3, (gay):2, (dee):1],
   (ian): [(hope):10, (cath):9, (dee):8, (gay):7, (bea):6, (abi):5, (fay):4, (ivy):3, (jan):2, (eve):1],
   (jon): [(abi):10, (fay):9, (jan):8, (gay):7, (eve):6, (bea):5, (dee):4, (cath):3, (ivy):2, (hope):1],

]

Map<Woman,List<Man>> womansManRanking = [

   (abi): [(bob):10, (fred):9, (jon):8, (gav):7, (ian):6, (abe):5, (dan):4, (ed):3, (col):2, (hal):1],
   (bea): [(bob):10, (abe):9, (col):8, (fred):7, (gav):6, (dan):5, (ian):4, (ed):3, (jon):2, (hal):1],
   (cath):[(fred):10, (bob):9, (ed):8, (gav):7, (hal):6, (col):5, (ian):4, (abe):3, (dan):2, (jon):1],
   (dee): [(fred):10, (jon):9, (col):8, (abe):7, (ian):6, (hal):5, (gav):4, (dan):3, (bob):2, (ed):1],
   (eve): [(jon):10, (hal):9, (fred):8, (dan):7, (abe):6, (gav):5, (col):4, (ed):3, (ian):2, (bob):1],
   (fay): [(bob):10, (abe):9, (ed):8, (ian):7, (jon):6, (dan):5, (fred):4, (gav):3, (col):2, (hal):1],
   (gay): [(jon):10, (gav):9, (hal):8, (fred):7, (bob):6, (abe):5, (col):4, (ed):3, (dan):2, (ian):1],
   (hope):[(gav):10, (jon):9, (bob):8, (abe):7, (ian):6, (dan):5, (hal):4, (ed):3, (col):2, (fred):1],
   (ivy): [(ian):10, (col):9, (hal):8, (gav):7, (fred):6, (bob):5, (abe):4, (ed):3, (jon):2, (dan):1],
   (jan): [(ed):10, (hal):9, (gav):8, (abe):7, (bob):6, (jon):5, (col):4, (ian):3, (fred):2, (dan):1],

]

// STABLE test Map<Woman,Man> matches = match(mansWomanRanking, womansManRanking) matches.each { w, m ->

   println "${w} (his '${mansWomanRanking[m][w]}' girl) is engaged to ${m} (her '${womansManRanking[w][m]}' guy)"

} assert matches.keySet() == Woman.values() as Set assert matches.values() as Set == Man.values() as Set println

assert isStable(matches, mansWomanRanking, womansManRanking)

// PERTURBED test println 'Swapping partners now ...' def temp = matches[abi] matches[abi] = matches[bea] matches[bea] = temp matches.each { w, m ->

   println "${w} (his '${mansWomanRanking[m][w]}' girl) is engaged to ${m} (her '${womansManRanking[w][m]}' guy)"

} println

assert ! isStable(matches, mansWomanRanking, womansManRanking)</lang>

Output:
abi (his '10' girl) is engaged to jon (her '8' guy)
bea (his '10' girl) is engaged to fred (her '7' guy)
cath (his '10' girl) is engaged to bob (her '9' guy)
dee (his '7' girl) is engaged to col (her '8' guy)
eve (his '9' girl) is engaged to hal (her '9' guy)
fay (his '9' girl) is engaged to dan (her '5' guy)
gay (his '10' girl) is engaged to gav (her '9' guy)
hope (his '10' girl) is engaged to ian (her '6' guy)
ivy (his '7' girl) is engaged to abe (her '4' guy)
jan (his '10' girl) is engaged to ed (her '10' guy)

Swapping partners now ...
abi (his '9' girl) is engaged to fred (her '9' guy)
bea (his '5' girl) is engaged to jon (her '2' guy)
cath (his '10' girl) is engaged to bob (her '9' guy)
dee (his '7' girl) is engaged to col (her '8' guy)
eve (his '9' girl) is engaged to hal (her '9' guy)
fay (his '9' girl) is engaged to dan (her '5' guy)
gay (his '10' girl) is engaged to gav (her '9' guy)
hope (his '10' girl) is engaged to ian (her '6' guy)
ivy (his '7' girl) is engaged to abe (her '4' guy)
jan (his '10' girl) is engaged to ed (her '10' guy)

O. M. G. ... bea likes fred better than jon, and fred likes bea better than abi!
                            I am TOTALLY 'shipping fred and bea now!
O. M. G. ... fred likes bea better than abi, and bea likes fred better than jon!
                            I am TOTALLY 'shipping bea and fred now!
O. M. G. ... jon likes eve better than bea, and eve likes jon better than hal!
                            I am TOTALLY 'shipping eve and jon now!
O. M. G. ... jon likes fay better than bea, and fay likes jon better than dan!
                            I am TOTALLY 'shipping fay and jon now!
O. M. G. ... jon likes gay better than bea, and gay likes jon better than gav!
                            I am TOTALLY 'shipping gay and jon now!

Haskell

The solution

The Gale/Shapley algorithm is formulated via iterative changing of the state. In Haskell it is possible to implement this approach by pure function iterations.

The state here consists of the list of free guys and associative preferences lists for guys and girls correspondingly. In order to simplify the access to elements of the state we use lenses.

<lang haskell>{-# LANGUAGE TemplateHaskell #-} import Lens.Micro import Lens.Micro.TH import Data.List (union, delete)

type Preferences a = (a, [a]) type Couple a = (a,a) data State a = State { _freeGuys :: [a]

                    , _guys :: [Preferences a]
                    , _girls :: [Preferences a]}

makeLenses State</lang>

Lenses allow us to get access to each person in the state, and even to the associated preference list:

<lang Haskell>name n = lens get set

 where get = head . dropWhile ((/= n).fst)
       set assoc (_,v) = let (prev, _:post) = break ((== n).fst) assoc
                     in prev ++ (n, v):post

fianceesOf n = guys.name n._2 fiancesOf n = girls.name n._2</lang>

Note that in following we use lens operators:

 ^.  -- access to a field
 %~  -- modification of a field
 .~  -- setting a field the value

Further we use a trick: guys list girls in a descending order of preference (the most liked is the first), while girls expect guys in opposite order -- the most liked is the last. In any case, we assume that the current best choice for guys and for girls is expected to appear on the top of their preference lists.

With these tools and notes we are ready to implement the Gale/Shapley algorithm and the stability test as they are given in a textbook:

<lang Haskell>stableMatching :: Eq a => State a -> [Couple a] stableMatching = getPairs . iterateUntil (null._freeGuys) step

 where
   iterateUntil p f = head . dropWhile (not . p) . iterate f
   getPairs s = map (_2 %~ head) $ s^.guys 

step :: Eq a => State a -> State a step s = foldl propose s (s^.freeGuys)

 where
   propose s guy =
     let girl                = s^.fianceesOf guy & head
         bestGuy : otherGuys = s^.fiancesOf girl
         modify
           | guy == bestGuy       = freeGuys %~ delete guy
           | guy `elem` otherGuys = (fiancesOf girl %~ dropWhile (/= guy)) .
                                    (freeGuys %~ guy `replaceBy` bestGuy)
           | otherwise            = fianceesOf guy %~ tail
     in modify s
   replaceBy x y [] = []
   replaceBy x y (h:t) | h == x = y:t
                       | otherwise = h:replaceBy x y t

unstablePairs :: Eq a => State a -> [Couple a] -> [(Couple a, Couple a)] unstablePairs s pairs =

 [ ((m1, w1), (m2,w2)) | (m1, w1) <- pairs
                       , (m2,w2) <- pairs
                       , m1 /= m2
                       , let fm = s^.fianceesOf m1
                       , elemIndex w2 fm < elemIndex w1 fm
                       , let fw = s^.fiancesOf w2
                       , elemIndex m2 fw < elemIndex m1 fw ]</lang>

This solution works not only for strings, but for any equable data.

The task

Here are the given preferences:

<lang Haskell>guys0 =

 [("abe", ["abi", "eve", "cath", "ivy", "jan", "dee", "fay", "bea", "hope", "gay"]),
  ("bob", ["cath", "hope", "abi", "dee", "eve", "fay", "bea", "jan", "ivy", "gay"]),
  ("col", ["hope", "eve", "abi", "dee", "bea", "fay", "ivy", "gay", "cath", "jan"]),
  ("dan", ["ivy", "fay", "dee", "gay", "hope", "eve", "jan", "bea", "cath", "abi"]),
  ("ed",  ["jan", "dee", "bea", "cath", "fay", "eve", "abi", "ivy", "hope", "gay"]),
  ("fred",["bea", "abi", "dee", "gay", "eve", "ivy", "cath", "jan", "hope", "fay"]),
  ("gav", ["gay", "eve", "ivy", "bea", "cath", "abi", "dee", "hope", "jan", "fay"]),
  ("hal", ["abi", "eve", "hope", "fay", "ivy", "cath", "jan", "bea", "gay", "dee"]),
  ("ian", ["hope", "cath", "dee", "gay", "bea", "abi", "fay", "ivy", "jan", "eve"]),
  ("jon", ["abi", "fay", "jan", "gay", "eve", "bea", "dee", "cath", "ivy", "hope"])]
 

girls0 =

 [("abi",  ["bob", "fred", "jon", "gav", "ian", "abe", "dan", "ed", "col", "hal"]),
  ("bea",  ["bob", "abe", "col", "fred", "gav", "dan", "ian", "ed", "jon", "hal"]),
  ("cath", ["fred", "bob", "ed", "gav", "hal", "col", "ian", "abe", "dan", "jon"]),
  ("dee",  ["fred", "jon", "col", "abe", "ian", "hal", "gav", "dan", "bob", "ed"]),
  ("eve",  ["jon", "hal", "fred", "dan", "abe", "gav", "col", "ed", "ian", "bob"]),
  ("fay",  ["bob", "abe", "ed", "ian", "jon", "dan", "fred", "gav", "col", "hal"]),
  ("gay",  ["jon", "gav", "hal", "fred", "bob", "abe", "col", "ed", "dan", "ian"]),
  ("hope", ["gav", "jon", "bob", "abe", "ian", "dan", "hal", "ed", "col", "fred"]),
  ("ivy",  ["ian", "col", "hal", "gav", "fred", "bob", "abe", "ed", "jon", "dan"]),
  ("jan",  ["ed", "hal", "gav", "abe", "bob", "jon", "col", "ian", "fred", "dan"])]</lang>
  

The initial state:

<lang Haskell>s0 = State (fst <$> guys0) guys0 ((_2 %~ reverse) <$> girls0)</lang>

And the solution:

λ> let pairs = stableMatching s0
λ> mapM_ print pairs
("abe","ivy")
("bob","cath")
("col","dee")
("dan","fay")
("ed","jan")
("fred","bea")
("gav","gay")
("hal","eve")
("ian","hope")
("jon","abi")
λ> unstablePairs s0 pairs
[]

Lets' make some perturbations: swap fiancees of abe and bob:

λ> let fiance n = name n._2
λ> let pairs' = pairs & (fiance "abe" .~ "cath") & (fiance "bob" .~ "ivy")
λ> mapM_ print $ unstablePairs s0 pairs'
(("bob","ivy"),("abe","cath"))
(("bob","ivy"),("dan","fay"))
(("bob","ivy"),("fred","bea"))
(("bob","ivy"),("ian","hope"))
(("bob","ivy"),("jon","abi"))

Icon and Unicon

<lang Icon>link printf

procedure main()

  smd := IsStable(ShowEngaged(StableMatching(setup())))   
  IsStable(ShowEngaged(Swap(\smd,smd.women[1],smd.women[2]))) 

end

procedure index(L,x) #: return index of value or fail

  return ( L[i := 1 to *L] === x, i)

end

procedure ShowEngaged(smd) #: Show who's hooked up

  printf("\nEngagements:\n")
  every w := !smd.women do
     printf("%s is engaged to %s\n",w,smd.engaged[w])
  return smd

end

procedure Swap(smd,x0,x1) #: swap two couples by m or w

  printf("\nSwapping %s and %s\n",x0,x1)
  e := smd.engaged
  e[x0] :=: e[x1]                           # swap partners
  e[e[x0]] := e[e[x1]]
  return smd

end

procedure IsStable(smd) #: validate stability

  stable := 1                                               # assumption
  printf("\n")
  every mp := smd.prefs[m := !smd.men] &                    # man & pref
        w := mp[index(mp,smd.engaged[m])-1 to 1 by -1] do { # better choices 
     wp := smd.prefs[w]                                     # her choices
     if index(wp,smd.engaged[w]) > index(wp,m) then {
        printf("Engagement of %s to %s is unstable.\n",w,m)
        stable := &null                                     # broken
        }
     }
  if \stable then {
     printf("Engagments are all stable.\n")
     return smd
     }

end

procedure StableMatching(smd) #: match making

  freemen   := copy(smd.men)                # Initialize all m memberof M 
  freewomen := set(smd.women)               # ... and w memberof W to free
  every (prefmen := table())[m := !freemen] := copy(smd.prefs[m])
  smd.engaged := engaged := table()
  printf("\nMatching:\n")   
  while m := get(freemen) do {                 # next freeman
     while w := get(prefmen[m]) do  {          # . with prpoposals left
        if member(freewomen,w) then {          # . . is she free?
           engaged[m] := w                     # . . . (m, w) 
           engaged[w] := m
           delete(freewomen,w)
           printf("%s accepted %s's proposal\n",w,m)
           break
           }
        else {                                 # . . no, she's engaged         
           m0 := engaged[w]                    #     to m0                  
           if index(smd.prefs[w],m) < index(smd.prefs[w],m0) then {  
              engaged[m] := w                  # (m, w) become engaged
              engaged[w] := m
              delete(freewomen,w)
              engaged[m0] := &null             # m' becomes free
              put(freemen,m0)   
              printf("%s chose %s over %s\n",w,m,m0)
              break
              }
           else next                          # she's happier as is 
        }
     }
  }
  return smd

end

record sm_data(men,women,prefs,engaged) #: everyones data

procedure setup() #: setup everyones data

  X := sm_data()
  X.men   := ["abe","bob","col","dan","ed","fred","gav","hal","ian","jon"]
  X.women := ["abi","bea","cath","dee","eve","fay","gay","hope","ivy","jan"]
  
  if *X.men ~= *(M := set(X.men)) then runerr(500,X.men)       # duplicate? 
  if *X.women ~= *(W := set(X.women)) then runerr(500,X.women) # duplicate?
  if *(B := M**W) ~= 0 then runerr(500,B)                      # intersect?
  
  X.prefs := p := table()
  
  p["abe"]  := ["abi","eve","cath","ivy","jan","dee","fay","bea","hope","gay"]
  p["bob"]  := ["cath","hope","abi","dee","eve","fay","bea","jan","ivy","gay"]
  p["col"]  := ["hope","eve","abi","dee","bea","fay","ivy","gay","cath","jan"]
  p["dan"]  := ["ivy","fay","dee","gay","hope","eve","jan","bea","cath","abi"]
  p["ed"]   := ["jan","dee","bea","cath","fay","eve","abi","ivy","hope","gay"]
  p["fred"] := ["bea","abi","dee","gay","eve","ivy","cath","jan","hope","fay"]
  p["gav"]  := ["gay","eve","ivy","bea","cath","abi","dee","hope","jan","fay"]
  p["hal"]  := ["abi","eve","hope","fay","ivy","cath","jan","bea","gay","dee"]
  p["ian"]  := ["hope","cath","dee","gay","bea","abi","fay","ivy","jan","eve"]
  p["jon"]  := ["abi","fay","jan","gay","eve","bea","dee","cath","ivy","hope"]
  
  p["abi"]  := ["bob","fred","jon","gav","ian","abe","dan","ed","col","hal"]
  p["bea"]  := ["bob","abe","col","fred","gav","dan","ian","ed","jon","hal"]
  p["cath"] := ["fred","bob","ed","gav","hal","col","ian","abe","dan","jon"]
  p["dee"]  := ["fred","jon","col","abe","ian","hal","gav","dan","bob","ed"]
  p["eve"]  := ["jon","hal","fred","dan","abe","gav","col","ed","ian","bob"]
  p["fay"]  := ["bob","abe","ed","ian","jon","dan","fred","gav","col","hal"]
  p["gay"]  := ["jon","gav","hal","fred","bob","abe","col","ed","dan","ian"]
  p["hope"] := ["gav","jon","bob","abe","ian","dan","hal","ed","col","fred"]
  p["ivy"]  := ["ian","col","hal","gav","fred","bob","abe","ed","jon","dan"]
  p["jan"]  := ["ed","hal","gav","abe","bob","jon","col","ian","fred","dan"]
  
  return X

end</lang>

printf.icn provides formatting

Output:
Matching:
abi accepted abe's proposal
cath accepted bob's proposal
hope accepted col's proposal
ivy accepted dan's proposal
jan accepted ed's proposal
bea accepted fred's proposal
gay accepted gav's proposal
eve accepted hal's proposal
hope chose ian over col
abi chose jon over abe
dee accepted col's proposal
ivy chose abe over dan
fay accepted dan's proposal

Engagements:
abi is engaged to jon
bea is engaged to fred
cath is engaged to bob
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to abe
jan is engaged to ed

Engagments are all stable.

Swapping abi and bea

Engagements:
abi is engaged to fred
bea is engaged to jon
cath is engaged to bob
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to abe
jan is engaged to ed

Engagement of bea to fred is unstable.

J

<lang j>Mraw=: ;: ;._2 noun define -. ':,'

 abe: abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay
 bob: cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay
 col: hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan
 dan: ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi
  ed: jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay
fred: bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay
 gav: gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay
 hal: abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee
 ian: hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve
 jon: abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope

)

Fraw=: ;: ;._2 noun define -. ':,'

 abi: bob, fred, jon, gav, ian, abe, dan, ed, col, hal
 bea: bob, abe, col, fred, gav, dan, ian, ed, jon, hal
cath: fred, bob, ed, gav, hal, col, ian, abe, dan, jon
 dee: fred, jon, col, abe, ian, hal, gav, dan, bob, ed
 eve: jon, hal, fred, dan, abe, gav, col, ed, ian, bob
 fay: bob, abe, ed, ian, jon, dan, fred, gav, col, hal
 gay: jon, gav, hal, fred, bob, abe, col, ed, dan, ian
hope: gav, jon, bob, abe, ian, dan, hal, ed, col, fred
 ivy: ian, col, hal, gav, fred, bob, abe, ed, jon, dan
 jan: ed, hal, gav, abe, bob, jon, col, ian, fred, dan

)

GuyNames=: {."1 Mraw GalNames=: {."1 Fraw

Mprefs=: GalNames i. }."1 Mraw Fprefs=: GuyNames i. }."1 Fraw

propose=: dyad define

 engaged=. x
 'guy gal'=. y
 if. gal e. engaged do.
   fiance=. engaged i. gal
   if. guy <&((gal{Fprefs)&i.) fiance do.
     engaged=. gal guy} _ fiance} engaged
   end.
 else.
   engaged=. gal guy} engaged
 end.
 engaged

)

matchMake=: monad define

 engaged=. _"0 GuyNames NB. initially no one is engaged
 fallback=. 0"0 engaged NB. and each guy will first propose to his favorite
 whilst. _ e. engaged do.
   for_guy. I. _ = engaged do.
     next=. guy{fallback
     gal=. (<guy,next){Mprefs
     engaged=. engaged propose guy,gal
     fallback=. (next+1) guy} fallback
   end.
 end.
 GuyNames,:engaged{GalNames

)

checkStable=: monad define

 'guys gals'=. (GuyNames,:GalNames) i."1 y
 satisfied=. ] >: (<0 1) |: ]
 guyshappy=. satisfied (guys{Mprefs) i."1 0/ gals
 galshappy=. satisfied (gals{Fprefs) i."1 0/ guys
 unstable=. 4$.$.-. guyshappy +. |:galshappy
 if. bad=. 0 < #unstable do.
   smoutput 'Engagements preferred by both members to their current ones:'
   smoutput y {~"1 0"2 1 unstable
 end.
 assert-.bad

)</lang>

For most of this, males and females are both represented by indices. Rows of Mprefs are indexed by a male index and each contains a list female indices, in priority order. Rows of Fprefs are indexed by a female index and each contains a list male indices in priority order. These indices select the corresponding names from GuyNames and GalNames.

In matchMake (and propose), engaged identifies the gal each guy is engaged to (or _ if that guy is not engaged). And, fallback identifies the column which has the next gal, in Mprefs, for that guy to propose to.

Example use:

<lang j> matchMake ┌───┬────┬───┬───┬───┬────┬───┬───┬────┬───┐ │abe│bob │col│dan│ed │fred│gav│hal│ian │jon│ ├───┼────┼───┼───┼───┼────┼───┼───┼────┼───┤ │ivy│cath│dee│fay│jan│bea │gay│eve│hope│abi│ └───┴────┴───┴───┴───┴────┴───┴───┴────┴───┘</lang>

Stability check:

<lang j> checkStable matchMake

  </lang>

(no news is good news)

An altered result, and a stability check on it (showing what would happen for a bogus result):

<lang j> 0 105 A."_1 matchMake NB. swap abi and bea ┌───┬────┬───┬───┬───┬────┬───┬───┬────┬───┐ │abe│bob │col│dan│ed │fred│gav│hal│ian │jon│ ├───┼────┼───┼───┼───┼────┼───┼───┼────┼───┤ │ivy│cath│dee│fay│jan│abi │gay│eve│hope│bea│ └───┴────┴───┴───┴───┴────┴───┴───┴────┴───┘

  checkStable 0 105 A."_1 matchMake 

Engagements preferred by both members to their current ones: ┌────┬───┐ │fred│bea│ ├────┼───┤ │jon │fay│ ├────┼───┤ │jon │gay│ ├────┼───┤ │jon │eve│ └────┴───┘ |assertion failure: assert | assert-.bad</lang> As an aside, note that the guys fared much better than the gals here, with over half of the guys getting their first preference and only one gal getting her first preference. The worst match for any guy was fourth preference where the worst for any gal was seventh preference.

Java

This is not a direct translation of Python, but it's fairly close (especially the stability check). <lang java5>import java.util.*;

public class Stable {

   static List<String> guys = Arrays.asList(
           new String[]{
       "abe", "bob", "col", "dan", "ed", "fred", "gav", "hal", "ian", "jon"});
   static List<String> girls = Arrays.asList(
           new String[]{
       "abi", "bea", "cath", "dee", "eve", "fay", "gay", "hope", "ivy", "jan"});
   static Map<String, List<String>> guyPrefers =
           new HashMap<String, List<String>>(){{
       put("abe",
           Arrays.asList("abi", "eve", "cath", "ivy", "jan", "dee", "fay",
           "bea", "hope", "gay"));
       put("bob",
           Arrays.asList("cath", "hope", "abi", "dee", "eve", "fay", "bea",
           "jan", "ivy", "gay"));
       put("col",
           Arrays.asList("hope", "eve", "abi", "dee", "bea", "fay", "ivy",
           "gay", "cath", "jan"));
       put("dan",
           Arrays.asList("ivy", "fay", "dee", "gay", "hope", "eve", "jan",
           "bea", "cath", "abi"));
       put("ed",
           Arrays.asList("jan", "dee", "bea", "cath", "fay", "eve", "abi",
           "ivy", "hope", "gay"));
       put("fred",
           Arrays.asList("bea", "abi", "dee", "gay", "eve", "ivy", "cath",
           "jan", "hope", "fay"));
       put("gav",
           Arrays.asList("gay", "eve", "ivy", "bea", "cath", "abi", "dee",
           "hope", "jan", "fay"));
       put("hal",
           Arrays.asList("abi", "eve", "hope", "fay", "ivy", "cath", "jan",
           "bea", "gay", "dee"));
       put("ian",
           Arrays.asList("hope", "cath", "dee", "gay", "bea", "abi", "fay",
           "ivy", "jan", "eve"));
       put("jon",
           Arrays.asList("abi", "fay", "jan", "gay", "eve", "bea", "dee",
           "cath", "ivy", "hope"));
   }};
   static Map<String, List<String>> girlPrefers =
           new HashMap<String, List<String>>(){{
       put("abi",
           Arrays.asList("bob", "fred", "jon", "gav", "ian", "abe", "dan",
           "ed", "col", "hal"));
       put("bea",
           Arrays.asList("bob", "abe", "col", "fred", "gav", "dan", "ian",
           "ed", "jon", "hal"));
       put("cath",
           Arrays.asList("fred", "bob", "ed", "gav", "hal", "col", "ian",
           "abe", "dan", "jon"));
       put("dee",
           Arrays.asList("fred", "jon", "col", "abe", "ian", "hal", "gav",
           "dan", "bob", "ed"));
       put("eve",
           Arrays.asList("jon", "hal", "fred", "dan", "abe", "gav", "col",
           "ed", "ian", "bob"));
       put("fay",
           Arrays.asList("bob", "abe", "ed", "ian", "jon", "dan", "fred",
           "gav", "col", "hal"));
       put("gay",
           Arrays.asList("jon", "gav", "hal", "fred", "bob", "abe", "col",
           "ed", "dan", "ian"));
       put("hope",
           Arrays.asList("gav", "jon", "bob", "abe", "ian", "dan", "hal",
           "ed", "col", "fred"));
       put("ivy",
           Arrays.asList("ian", "col", "hal", "gav", "fred", "bob", "abe",
           "ed", "jon", "dan"));
       put("jan",
           Arrays.asList("ed", "hal", "gav", "abe", "bob", "jon", "col",
           "ian", "fred", "dan"));
   }};
   public static void main(String[] args){
       Map<String, String> matches = match(guys, guyPrefers, girlPrefers);
       for(Map.Entry<String, String> couple:matches.entrySet()){
           System.out.println(
                   couple.getKey() + " is engaged to " + couple.getValue());
       }
       if(checkMatches(guys, girls, matches, guyPrefers, girlPrefers)){
           System.out.println("Marriages are stable");
       }else{
           System.out.println("Marriages are unstable");
       }
       String tmp = matches.get(girls.get(0));
       matches.put(girls.get(0), matches.get(girls.get(1)));
       matches.put(girls.get(1), tmp);
       System.out.println(
               girls.get(0) +" and " + girls.get(1) + " have switched partners");
       if(checkMatches(guys, girls, matches, guyPrefers, girlPrefers)){
           System.out.println("Marriages are stable");
       }else{
           System.out.println("Marriages are unstable");
       }
   }
   private static Map<String, String> match(List<String> guys,
           Map<String, List<String>> guyPrefers,
           Map<String, List<String>> girlPrefers){
       Map<String, String> engagedTo = new TreeMap<String, String>();
       List<String> freeGuys = new LinkedList<String>();
       freeGuys.addAll(guys);
       while(!freeGuys.isEmpty()){
           String thisGuy = freeGuys.remove(0); //get a load of THIS guy
           List<String> thisGuyPrefers = guyPrefers.get(thisGuy);
           for(String girl:thisGuyPrefers){
               if(engagedTo.get(girl) == null){//girl is free
                   engagedTo.put(girl, thisGuy); //awww
                   break;
               }else{
                   String otherGuy = engagedTo.get(girl);
                   List<String> thisGirlPrefers = girlPrefers.get(girl);
                   if(thisGirlPrefers.indexOf(thisGuy) <
                           thisGirlPrefers.indexOf(otherGuy)){
                       //this girl prefers this guy to the guy she's engaged to
                       engagedTo.put(girl, thisGuy);
                       freeGuys.add(otherGuy);
                       break;
                   }//else no change...keep looking for this guy
               }
           }
       }
       return engagedTo;
   }
   private static boolean checkMatches(List<String> guys, List<String> girls,
           Map<String, String> matches, Map<String, List<String>> guyPrefers,
           Map<String, List<String>> girlPrefers) {
       if(!matches.keySet().containsAll(girls)){
           return false;
       }
       if(!matches.values().containsAll(guys)){
           return false;
       }
       Map<String, String> invertedMatches = new TreeMap<String, String>();
       for(Map.Entry<String, String> couple:matches.entrySet()){
           invertedMatches.put(couple.getValue(), couple.getKey());
       }
       for(Map.Entry<String, String> couple:matches.entrySet()){
           List<String> shePrefers = girlPrefers.get(couple.getKey());
           List<String> sheLikesBetter = new LinkedList<String>();
           sheLikesBetter.addAll(shePrefers.subList(0, shePrefers.indexOf(couple.getValue())));
           List<String> hePrefers = guyPrefers.get(couple.getValue());
           List<String> heLikesBetter = new LinkedList<String>();
           heLikesBetter.addAll(hePrefers.subList(0, hePrefers.indexOf(couple.getKey())));
           for(String guy : sheLikesBetter){
               String guysFinace = invertedMatches.get(guy);
               List<String> thisGuyPrefers = guyPrefers.get(guy);
               if(thisGuyPrefers.indexOf(guysFinace) >
                       thisGuyPrefers.indexOf(couple.getKey())){
                   System.out.printf("%s likes %s better than %s and %s"
                           + " likes %s better than their current partner\n",
                      couple.getKey(), guy, couple.getValue(),
                      guy, couple.getKey());
                   return false;
               }
           }
           for(String girl : heLikesBetter){
               String girlsFinace = matches.get(girl);
               List<String> thisGirlPrefers = girlPrefers.get(girl);
               if(thisGirlPrefers.indexOf(girlsFinace) >
                       thisGirlPrefers.indexOf(couple.getValue())){
                   System.out.printf("%s likes %s better than %s and %s"
                           + " likes %s better than their current partner\n",
                      couple.getValue(), girl, couple.getKey(),
                      girl, couple.getValue());
                   return false;
               }
           }
       }
       return true;
   }

}</lang>

Output:
abi is engaged to jon
bea is engaged to fred
cath is engaged to bob
dee is engaged to col
eve is engaged to hal
fay is engaged to dan
gay is engaged to gav
hope is engaged to ian
ivy is engaged to abe
jan is engaged to ed
Marriages are stable
abi and bea have switched partners
fred likes bea better than abi and bea likes fred better than their current partner
Marriages are unstable

JavaScript

<lang javascript>function Person(name) {

   var candidateIndex = 0;
   this.name = name;
   this.fiance = null;
   this.candidates = [];
   this.rank = function(p) {
       for (i = 0; i < this.candidates.length; i++)
           if (this.candidates[i] === p) return i;
       return this.candidates.length + 1;
   }
   this.prefers = function(p) {
       return this.rank(p) < this.rank(this.fiance);
   }
   this.nextCandidate = function() {
       if (candidateIndex >= this.candidates.length) return null;
       return this.candidates[candidateIndex++];
   }
   this.engageTo = function(p) {
       if (p.fiance) p.fiance.fiance = null;
       p.fiance = this;
       if (this.fiance) this.fiance.fiance = null;
       this.fiance = p;
   }
   this.swapWith = function(p) {
       console.log("%s & %s swap partners", this.name, p.name);
       var thisFiance = this.fiance;
       var pFiance = p.fiance;
       this.engageTo(pFiance);
       p.engageTo(thisFiance);
   }

}

function isStable(guys, gals) {

   for (var i = 0; i < guys.length; i++)
       for (var j = 0; j < gals.length; j++)
           if (guys[i].prefers(gals[j]) && gals[j].prefers(guys[i]))
               return false;
   return true;

}

function engageEveryone(guys) {

   var done;
   do {
       done = true;
       for (var i = 0; i < guys.length; i++) {
           var guy = guys[i];
           if (!guy.fiance) {
               done = false;
               var gal = guy.nextCandidate();
               if (!gal.fiance || gal.prefers(guy))
                   guy.engageTo(gal);
           }
       }
   } while (!done);

}

function doMarriage() {

   var abe  = new Person("Abe");
   var bob  = new Person("Bob");
   var col  = new Person("Col");
   var dan  = new Person("Dan");
   var ed   = new Person("Ed");
   var fred = new Person("Fred");
   var gav  = new Person("Gav");
   var hal  = new Person("Hal");
   var ian  = new Person("Ian");
   var jon  = new Person("Jon");
   var abi  = new Person("Abi");
   var bea  = new Person("Bea");
   var cath = new Person("Cath");
   var dee  = new Person("Dee");
   var eve  = new Person("Eve");
   var fay  = new Person("Fay");
   var gay  = new Person("Gay");
   var hope = new Person("Hope");
   var ivy  = new Person("Ivy");
   var jan  = new Person("Jan");
   abe.candidates  = [abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay];
   bob.candidates  = [cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay];
   col.candidates  = [hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan];
   dan.candidates  = [ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi];
   ed.candidates   = [jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay];
   fred.candidates = [bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay];
   gav.candidates  = [gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay];
   hal.candidates  = [abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee];
   ian.candidates  = [hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve];
   jon.candidates  = [abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope];
   abi.candidates  = [bob, fred, jon, gav, ian, abe, dan, ed, col, hal];
   bea.candidates  = [bob, abe, col, fred, gav, dan, ian, ed, jon, hal];
   cath.candidates = [fred, bob, ed, gav, hal, col, ian, abe, dan, jon];
   dee.candidates  = [fred, jon, col, abe, ian, hal, gav, dan, bob, ed];
   eve.candidates  = [jon, hal, fred, dan, abe, gav, col, ed, ian, bob];
   fay.candidates  = [bob, abe, ed, ian, jon, dan, fred, gav, col, hal];
   gay.candidates  = [jon, gav, hal, fred, bob, abe, col, ed, dan, ian];
   hope.candidates = [gav, jon, bob, abe, ian, dan, hal, ed, col, fred];
   ivy.candidates  = [ian, col, hal, gav, fred, bob, abe, ed, jon, dan];
   jan.candidates  = [ed, hal, gav, abe, bob, jon, col, ian, fred, dan];
   var guys = [abe, bob, col, dan, ed, fred, gav, hal, ian, jon];
   var gals = [abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan];
   engageEveryone(guys);
   for (var i = 0; i < guys.length; i++) {
       console.log("%s is engaged to %s", guys[i].name, guys[i].fiance.name);
   }
   console.log("Stable = %s", isStable(guys, gals) ? "Yes" : "No");
   jon.swapWith(fred);
   console.log("Stable = %s", isStable(guys, gals) ? "Yes" : "No");

}

doMarriage(); </lang>

Output:
Abe is engaged to Ivy
Bob is engaged to Cath
Col is engaged to Dee
Dan is engaged to Fay
Ed is engaged to Jan
Fred is engaged to Bea
Gav is engaged to Gay
Hal is engaged to Eve
Ian is engaged to Hope
Jon is engaged to Abi
Stable = Yes
Jon & Fred swap partners
Stable = No

Kotlin

Translation of: Java

<lang scala>import java.util.*

class People(val map: Map<String, Array<String>>) {

   operator fun get(name: String) = map[name]
   val names: List<String> by lazy { map.keys.toList() }
   fun preferences(k: String, v: String): List<String> {
       val prefers = get(k)!!
       return ArrayList<String>(prefers.slice(0..prefers.indexOf(v)))
   }

}

class EngagementRegistry() : TreeMap<String, String>() {

   constructor(guys: People, girls: People) : this() {
       val freeGuys = guys.names.toMutableList()
       while (freeGuys.any()) {
           val guy = freeGuys.removeAt(0) // get a load of THIS guy
           val guy_p = guys[guy]!!
           for (girl in guy_p)
               if (this[girl] == null) {
                   this[girl] = guy  // girl is free
                   break
               } else {
                   val other = this[girl]!!
                   val girl_p = girls[girl]!!
                   if (girl_p.indexOf(guy) < girl_p.indexOf(other)) {
                       this[girl] = guy // this girl prefers this guy to the guy she's engaged to
                       freeGuys += other
                       break
                   } // else no change... keep looking for this guy
               }
       }
   }
   override fun toString(): String {
       val s = StringBuilder()
       for ((k, v) in this) s.append("$k is engaged to $v\n")
       return s.toString()
   }
   fun analyse(guys: People, girls: People) {
       if (check(guys, girls))
           println("Marriages are stable")
       else
           println("Marriages are unstable")
   }
   fun swap(girls: People, i: Int, j: Int) {
       val n1 = girls.names[i]
       val n2 = girls.names[j]
       val g0 = this[n1]!!
       val g1 = this[n2]!!
       this[n1] = g1
       this[n2] = g0
       println("$n1 and $n2 have switched partners")
   }
   private fun check(guys: People, girls: People): Boolean {
       val guy_names = guys.names
       val girl_names = girls.names
       if (!keys.containsAll(girl_names) or !values.containsAll(guy_names))
           return false
       val invertedMatches = TreeMap<String, String>()
       for ((k, v) in this) invertedMatches[v] = k
       for ((k, v) in this) {
           val sheLikesBetter = girls.preferences(k, v)
           val heLikesBetter = guys.preferences(v, k)
           for (guy in sheLikesBetter) {
               val fiance = invertedMatches[guy]
               val guy_p = guys[guy]!!
               if (guy_p.indexOf(fiance) > guy_p.indexOf(k)) {
                   println("$k likes $guy better than $v and $guy likes $k better than their current partner")
                   return false
               }
           }
           for (girl in heLikesBetter) {
               val fiance = get(girl)
               val girl_p = girls[girl]!!
               if (girl_p.indexOf(fiance) > girl_p.indexOf(v)) {
                   println("$v likes $girl better than $k and $girl likes $v better than their current partner")
                   return false
               }
           }
       }
       return true
   }

}

fun main(args: Array<String>) {

   val guys = People(mapOf("abe" to arrayOf("abi", "eve", "cath", "ivy", "jan", "dee", "fay", "bea", "hope", "gay"),
           "bob" to arrayOf("cath", "hope", "abi", "dee", "eve", "fay", "bea", "jan", "ivy", "gay"),
           "col" to arrayOf("hope", "eve", "abi", "dee", "bea", "fay", "ivy", "gay", "cath", "jan"),
           "dan" to arrayOf("ivy", "fay", "dee", "gay", "hope", "eve", "jan", "bea", "cath", "abi"),
           "ed" to arrayOf("jan", "dee", "bea", "cath", "fay", "eve", "abi", "ivy", "hope", "gay"),
           "fred" to arrayOf("bea", "abi", "dee", "gay", "eve", "ivy", "cath", "jan", "hope", "fay"),
           "gav" to arrayOf("gay", "eve", "ivy", "bea", "cath", "abi", "dee", "hope", "jan", "fay"),
           "hal" to arrayOf("abi", "eve", "hope", "fay", "ivy", "cath", "jan", "bea", "gay", "dee"),
           "ian" to arrayOf("hope", "cath", "dee", "gay", "bea", "abi", "fay", "ivy", "jan", "eve"),
           "jon" to arrayOf("abi", "fay", "jan", "gay", "eve", "bea", "dee", "cath", "ivy", "hope")))
   val girls = People(mapOf("abi" to arrayOf("bob", "fred", "jon", "gav", "ian", "abe", "dan", "ed", "col", "hal"),
           "bea" to arrayOf("bob", "abe", "col", "fred", "gav", "dan", "ian", "ed", "jon", "hal"),
           "cath" to arrayOf("fred", "bob", "ed", "gav", "hal", "col", "ian", "abe", "dan", "jon"),
           "dee" to arrayOf("fred", "jon", "col", "abe", "ian", "hal", "gav", "dan", "bob", "ed"),
           "eve" to arrayOf("jon", "hal", "fred", "dan", "abe", "gav", "col", "ed", "ian", "bob"),
           "fay" to arrayOf("bob", "abe", "ed", "ian", "jon", "dan", "fred", "gav", "col", "hal"),
           "gay" to arrayOf("jon", "gav", "hal", "fred", "bob", "abe", "col", "ed", "dan", "ian"),
           "hope" to arrayOf("gav", "jon", "bob", "abe", "ian", "dan", "hal", "ed", "col", "fred"),
           "ivy" to arrayOf("ian", "col", "hal", "gav", "fred", "bob", "abe", "ed", "jon", "dan"),
           "jan" to arrayOf("ed", "hal", "gav", "abe", "bob", "jon", "col", "ian", "fred", "dan")))
   with(EngagementRegistry(guys, girls)) {
       print(this)
       analyse(guys, girls)
       swap(girls, 0, 1)
       analyse(guys, girls)
   }

}</lang>

Output:

See Java output.

Lua

Translation of: C#

<lang lua>local Person = {} Person.__index = Person

function Person.new(inName)

   local o = {
       name            = inName,
       prefs           = nil,
       fiance          = nil,
       _candidateIndex = 1,
   }
   return setmetatable(o, Person)

end

function Person:indexOf(other)

   for i, p in pairs(self.prefs) do
       if p == other then return i end
   end
   return 999

end

function Person:prefers(other)

   return self:indexOf(other) < self:indexOf(self.fiance)

end

function Person:nextCandidateNotYetProposedTo()

   if self._candidateIndex >= #self.prefs then return nil end
   local c = self.prefs[self._candidateIndex];
   self._candidateIndex = self._candidateIndex + 1
   return c;

end

function Person:engageTo(other)

   if other.fiance then
       other.fiance.fiance = nil
   end
   other.fiance = self
   if self.fiance then
       self.fiance.fiance = nil
   end
   self.fiance = other;

end

local function isStable(men)

   local women = men[1].prefs
   local stable = true
   for _, guy in pairs(men) do
       for _, gal in pairs(women) do
           if guy:prefers(gal) and gal:prefers(guy) then
               stable = false
               print(guy.name .. ' and ' .. gal.name ..
                     ' prefer each other over their partners ' ..
                     guy.fiance.name .. ' and ' .. gal.fiance.name)
           end
       end
   end
   return stable

end

local abe = Person.new("Abe") local bob = Person.new("Bob") local col = Person.new("Col") local dan = Person.new("Dan") local ed = Person.new("Ed") local fred = Person.new("Fred") local gav = Person.new("Gav") local hal = Person.new("Hal") local ian = Person.new("Ian") local jon = Person.new("Jon")

local abi = Person.new("Abi") local bea = Person.new("Bea") local cath = Person.new("Cath") local dee = Person.new("Dee") local eve = Person.new("Eve") local fay = Person.new("Fay") local gay = Person.new("Gay") local hope = Person.new("Hope") local ivy = Person.new("Ivy") local jan = Person.new("Jan")

abe.prefs = { abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay } bob.prefs = { cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay } col.prefs = { hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan } dan.prefs = { ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi } ed.prefs = { jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay } fred.prefs = { bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay } gav.prefs = { gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay } hal.prefs = { abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee } ian.prefs = { hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve } jon.prefs = { abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope }

abi.prefs = { bob, fred, jon, gav, ian, abe, dan, ed, col, hal } bea.prefs = { bob, abe, col, fred, gav, dan, ian, ed, jon, hal } cath.prefs = { fred, bob, ed, gav, hal, col, ian, abe, dan, jon } dee.prefs = { fred, jon, col, abe, ian, hal, gav, dan, bob, ed } eve.prefs = { jon, hal, fred, dan, abe, gav, col, ed, ian, bob } fay.prefs = { bob, abe, ed, ian, jon, dan, fred, gav, col, hal } gay.prefs = { jon, gav, hal, fred, bob, abe, col, ed, dan, ian } hope.prefs = { gav, jon, bob, abe, ian, dan, hal, ed, col, fred } ivy.prefs = { ian, col, hal, gav, fred, bob, abe, ed, jon, dan } jan.prefs = { ed, hal, gav, abe, bob, jon, col, ian, fred, dan }

local men = abi.prefs local freeMenCount = #men while freeMenCount > 0 do

   for _, guy in pairs(men) do
       if not guy.fiance then
           local gal = guy:nextCandidateNotYetProposedTo()
           if not gal.fiance then
               guy:engageTo(gal)
               freeMenCount = freeMenCount - 1
           elseif gal:prefers(guy) then
               guy:engageTo(gal)
           end
       end
   end

end

print(' ') for _, guy in pairs(men) do

   print(guy.name .. ' is engaged to ' .. guy.fiance.name)

end print('Stable: ', isStable(men))

print(' ') print('Switching ' .. fred.name .. "'s & " .. jon.name .. "'s partners") jon.fiance, fred.fiance = fred.fiance, jon.fiance print('Stable: ', isStable(men)) </lang>

Output:
Bob is engaged to Cath
Fred is engaged to Bea
Jon is engaged to Abi
Gav is engaged to Gay
Ian is engaged to Hope
Abe is engaged to Ivy
Dan is engaged to Fay
Ed is engaged to Jan
Col is engaged to Dee
Hal is engaged to Eve
Stable:   true

Switching Fred's & Jon's partners
Jon and Eve prefer each other over their partners Bea and Hal
Jon and Fay prefer each other over their partners Bea and Dan
Jon and Gay prefer each other over their partners Bea and Gav
Stable:   false

Objective-C

Works with: XCode 4.5.1

(The C# version is essentially the same as this.) <lang objc>//-------------------------------------------------------------------- // Person class

@interface Person : NSObject {

   NSUInteger _candidateIndex;

} @property (nonatomic, strong) NSString* name; @property (nonatomic, strong) NSArray* prefs; @property (nonatomic, weak) Person* fiance; @end

@implementation Person + (instancetype)named:(NSString *)name {

   return [[self alloc] initWithName:name];

} - (instancetype)initWithName:(NSString *)name {

   if ((self = [super init])) {
       _name = name;
       _prefs = nil;
       _fiance = nil;
       _candidateIndex = 0;
   }
   return self;

} - (BOOL)prefers:(Person *)p {

   return [_prefs indexOfObject:p] < [_prefs indexOfObject:_fiance];

} - (Person *)nextCandidateNotYetProposedTo {

   if (_candidateIndex >= _prefs.count) return nil;
   return _prefs[_candidateIndex++];

} - (void)engageTo:(Person *)p {

   if (p.fiance) p.fiance.fiance = nil;
   p.fiance = self;
   if (self.fiance) self.fiance.fiance = nil;
   self.fiance = p;

} - (NSString *)description {

   return _name;

} @end

//--------------------------------------------------------------------

BOOL isStable(NSArray *men) {

   NSArray *women = ((Person *)men[0]).prefs;
   for (Person *guy in men) {
       for (Person *gal in women) {
           if ([guy prefers:gal] && [gal prefers:guy])
               return NO;
       }
   }
   return YES;

}

//--------------------------------------------------------------------

void doMarriage() {

   Person *abe  = [Person named:@"abe"];
   Person *bob  = [Person named:@"bob"];
   Person *col  = [Person named:@"col"];
   Person *dan  = [Person named:@"dan"];
   Person *ed   = [Person named:@"ed"];
   Person *fred = [Person named:@"fred"];
   Person *gav  = [Person named:@"gav"];
   Person *hal  = [Person named:@"hal"];
   Person *ian  = [Person named:@"ian"];
   Person *jon  = [Person named:@"jon"];
   Person *abi  = [Person named:@"abi"];
   Person *bea  = [Person named:@"bea"];
   Person *cath = [Person named:@"cath"];
   Person *dee  = [Person named:@"dee"];
   Person *eve  = [Person named:@"eve"];
   Person *fay  = [Person named:@"fay"];
   Person *gay  = [Person named:@"gay"];
   Person *hope = [Person named:@"hope"];
   Person *ivy  = [Person named:@"ivy"];
   Person *jan  = [Person named:@"jan"];
   
   abe.prefs  = @[ abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay ];
   bob.prefs  = @[ cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay ];
   col.prefs  = @[ hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan ];
   dan.prefs  = @[ ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi ];
   ed.prefs   = @[ jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay ];
   fred.prefs = @[ bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay ];
   gav.prefs  = @[ gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay ];
   hal.prefs  = @[ abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee ];
   ian.prefs  = @[ hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve ];
   jon.prefs  = @[ abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope ];
   abi.prefs  = @[ bob, fred, jon, gav, ian, abe, dan, ed, col, hal ];
   bea.prefs  = @[ bob, abe, col, fred, gav, dan, ian, ed, jon, hal ];
   cath.prefs = @[ fred, bob, ed, gav, hal, col, ian, abe, dan, jon ];
   dee.prefs  = @[ fred, jon, col, abe, ian, hal, gav, dan, bob, ed ];
   eve.prefs  = @[ jon, hal, fred, dan, abe, gav, col, ed, ian, bob ];
   fay.prefs  = @[ bob, abe, ed, ian, jon, dan, fred, gav, col, hal ];
   gay.prefs  = @[ jon, gav, hal, fred, bob, abe, col, ed, dan, ian ];
   hope.prefs = @[ gav, jon, bob, abe, ian, dan, hal, ed, col, fred ];
   ivy.prefs  = @[ ian, col, hal, gav, fred, bob, abe, ed, jon, dan ];
   jan.prefs  = @[ ed, hal, gav, abe, bob, jon, col, ian, fred, dan ];
   
   NSArray *men = abi.prefs;
   
   NSUInteger freeMenCount = men.count;
   while (freeMenCount > 0) {
       for (Person *guy in men) {
           if (guy.fiance == nil) {
               Person *gal = [guy nextCandidateNotYetProposedTo];
               if (gal.fiance == nil) {
                   [guy engageTo:gal];
                   freeMenCount--;
               } else if ([gal prefers:guy]) {
                   [guy engageTo:gal];
               }
           }
       }
   }
   
   for (Person *guy in men) {
       printf("%s is engaged to %s\n", [guy.name UTF8String], [guy.fiance.name UTF8String]);
   }
   printf("Stable = %d\n", (int)isStable(men));
   printf("\nSwitching fred & jon's partners\n");
   [fred engageTo:abi];
   [jon engageTo:bea];
   printf("Stable = %d\n", (int)isStable(men));

}

//--------------------------------------------------------------------

int main(int argc, const char * argv[]) {

   @autoreleasepool {
       doMarriage();
   }
   return 0;

}</lang>

Output:
bob is engaged to cath
fred is engaged to bea
jon is engaged to abi
gav is engaged to gay
ian is engaged to hope
abe is engaged to ivy
dan is engaged to fay
ed is engaged to jan
col is engaged to dee
hal is engaged to eve
Stable = 1

Switching fred & jon's partners
Stable = 0

OCaml

<lang ocaml>let men = [

 "abe",  ["abi";"eve";"cath";"ivy";"jan";"dee";"fay";"bea";"hope";"gay"];
 "bob",  ["cath";"hope";"abi";"dee";"eve";"fay";"bea";"jan";"ivy";"gay"];
 "col",  ["hope";"eve";"abi";"dee";"bea";"fay";"ivy";"gay";"cath";"jan"];
 "dan",  ["ivy";"fay";"dee";"gay";"hope";"eve";"jan";"bea";"cath";"abi"];
 "ed",   ["jan";"dee";"bea";"cath";"fay";"eve";"abi";"ivy";"hope";"gay"];
 "fred", ["bea";"abi";"dee";"gay";"eve";"ivy";"cath";"jan";"hope";"fay"];
 "gav",  ["gay";"eve";"ivy";"bea";"cath";"abi";"dee";"hope";"jan";"fay"];
 "hal",  ["abi";"eve";"hope";"fay";"ivy";"cath";"jan";"bea";"gay";"dee"];
 "ian",  ["hope";"cath";"dee";"gay";"bea";"abi";"fay";"ivy";"jan";"eve"];
 "jon",  ["abi";"fay";"jan";"gay";"eve";"bea";"dee";"cath";"ivy";"hope"];

]

let women = [

 "abi",  ["bob";"fred";"jon";"gav";"ian";"abe";"dan";"ed";"col";"hal"];
 "bea",  ["bob";"abe";"col";"fred";"gav";"dan";"ian";"ed";"jon";"hal"];
 "cath", ["fred";"bob";"ed";"gav";"hal";"col";"ian";"abe";"dan";"jon"];
 "dee",  ["fred";"jon";"col";"abe";"ian";"hal";"gav";"dan";"bob";"ed"];
 "eve",  ["jon";"hal";"fred";"dan";"abe";"gav";"col";"ed";"ian";"bob"];
 "fay",  ["bob";"abe";"ed";"ian";"jon";"dan";"fred";"gav";"col";"hal"];
 "gay",  ["jon";"gav";"hal";"fred";"bob";"abe";"col";"ed";"dan";"ian"];
 "hope", ["gav";"jon";"bob";"abe";"ian";"dan";"hal";"ed";"col";"fred"];
 "ivy",  ["ian";"col";"hal";"gav";"fred";"bob";"abe";"ed";"jon";"dan"];
 "jan",  ["ed";"hal";"gav";"abe";"bob";"jon";"col";"ian";"fred";"dan"];

]

type woman_name = string type man_name = string

type man =

 { m_name: man_name;
   mutable free: bool;
   women_rank: woman_name list;
   has_proposed: (woman_name, unit) Hashtbl.t (* a set *)
 }

type woman =

 { w_name: woman_name;
   men_rank: man_name list;
   mutable engaged: man_name option
 }


let prefers w m1 m2 =

 (* returns true if w has a lower (better) rank for m1 than m2 *)
 let rec aux = function
 | [] -> invalid_arg "rank_cmp"
 | x::_ when x = m1 -> true
 | x::_ when x = m2 -> false
 | _::xs -> aux xs
 in
 aux w.men_rank

let take_while f lst =

 let rec aux acc = function
 | x::xs when f x -> aux (x::acc) xs
 | _ -> List.rev acc
 in
 aux [] lst

let more_ranked_than name =

 take_while ((<>) name)

let build_structs ~men ~women =

 List.map (fun (name, rank) ->
   { m_name = name;
     women_rank = rank;
     free = true;
     has_proposed = Hashtbl.create 42 }
 ) men,
 List.map (fun (name, rank) ->
   { w_name = name;
     men_rank = rank;
     engaged = None }
 ) women


let _stable_matching ms ws =

 let men_by_name = Hashtbl.create 42 in
 List.iter (fun m -> Hashtbl.add men_by_name m.m_name m) ms;
 let women_by_name = Hashtbl.create 42 in
 List.iter (fun w -> Hashtbl.add women_by_name w.w_name w) ws;
 try
   while true do
     (*TODO free men who still has some w to propose to *)
     let m = List.find (fun m -> m.free) ms in
     (* highest ranked woman who the man has not proposed to yet *)
     let w_name =
       List.find (fun w -> not (Hashtbl.mem m.has_proposed w)) m.women_rank in
     Hashtbl.add m.has_proposed w_name ();
     let w = Hashtbl.find women_by_name w_name in
     match w.engaged with
     | None -> (* w is free *)
         (* (m, w) become engaged *)
         w.engaged <- Some m.m_name;
         m.free <- false
     | Some m'_name -> (* some pair (m', w) already exists *)
         if prefers w m.m_name m'_name
         then begin (* w prefers m to m' *)
           w.engaged <- Some m.m_name;
           let m' = Hashtbl.find men_by_name m'_name in
           m'.free <- true;
           m.free <- false
         end
   done;
   assert false
 with Not_found -> ()


let stable_matching ~men ~women =

 let ms, ws = build_structs ~men ~women in
 _stable_matching ms ws;
 let some = function Some v -> v | None -> "" in
 List.map (fun w -> w.w_name, some w.engaged) ws


let is_stable ~men ~women eng =

 let ms, ws = build_structs ~men ~women in
 not (List.exists (fun (wn, mn) ->
     let m = List.find (fun m -> m.m_name = mn) ms in
     let prefered_women = more_ranked_than wn m.women_rank in
     List.exists (fun pref_w ->
       let w = List.find (fun w -> w.w_name = pref_w) ws in
       let eng_m = List.assoc pref_w eng in
       let prefered_men = more_ranked_than eng_m w.men_rank in
       List.mem m.m_name prefered_men (* exists unstable engagement *)
     ) prefered_women
   ) eng)


let perturb_engagements eng =

 Random.self_init();
 let eng = Array.of_list eng in
 let len = Array.length eng in
 for n = 1 to 3 do
   let i = Random.int len
   and j = Random.int len in
   let w1, m1 = eng.(i)
   and w2, m2 = eng.(j) in
   eng.(i) <- (w1, m2);
   eng.(j) <- (w2, m1);
 done;
 Array.to_list eng


let print engs =

 List.iter (fun (w,m) ->
   Printf.printf " %4s is engaged with %s\n" w m) engs;
 Printf.printf "# Engagements %s stable\n"
   (if is_stable ~men ~women engs then "are" else "are not")

let () =

 let engagements = stable_matching ~men ~women in
 print engagements;
 print_endline "========================";
 let engagements = perturb_engagements engagements in
 print engagements;
</lang>
Output:
  fay is engaged with dan
  ivy is engaged with abe
 cath is engaged with bob
  eve is engaged with hal
  abi is engaged with jon
  dee is engaged with col
 hope is engaged with ian
  gay is engaged with gav
  bea is engaged with fred
  jan is engaged with ed
# Engagements are stable
========================
  fay is engaged with abe
  ivy is engaged with dan
 cath is engaged with hal
  eve is engaged with bob
  abi is engaged with jon
  dee is engaged with col
 hope is engaged with ed
  gay is engaged with gav
  bea is engaged with fred
  jan is engaged with ian
# Engagements are not stable

Perl

<lang Perl>#!/usr/bin/env perl use strict; use warnings; use feature qw/say/; use List::Util qw(first);

my %Likes = (

 M => {
   abe  => [qw/ abi eve cath ivy jan dee fay bea hope gay /],
   bob  => [qw/ cath hope abi dee eve fay bea jan ivy gay /],
   col  => [qw/ hope eve abi dee bea fay ivy gay cath jan /],
   dan  => [qw/ ivy fay dee gay hope eve jan bea cath abi /],
   ed   => [qw/ jan dee bea cath fay eve abi ivy hope gay /],
   fred => [qw/ bea abi dee gay eve ivy cath jan hope fay /],
   gav  => [qw/ gay eve ivy bea cath abi dee hope jan fay /],
   hal  => [qw/ abi eve hope fay ivy cath jan bea gay dee /],
   ian  => [qw/ hope cath dee gay bea abi fay ivy jan eve /],
   jon  => [qw/ abi fay jan gay eve bea dee cath ivy hope /],
 },
 W => {
   abi  => [qw/ bob fred jon gav ian abe dan ed col hal /],
   bea  => [qw/ bob abe col fred gav dan ian ed jon hal /],
   cath => [qw/ fred bob ed gav hal col ian abe dan jon /],
   dee  => [qw/ fred jon col abe ian hal gav dan bob ed /],
   eve  => [qw/ jon hal fred dan abe gav col ed ian bob /],
   fay  => [qw/ bob abe ed ian jon dan fred gav col hal /],
   gay  => [qw/ jon gav hal fred bob abe col ed dan ian /],
   hope => [qw/ gav jon bob abe ian dan hal ed col fred /],
   ivy  => [qw/ ian col hal gav fred bob abe ed jon dan /],
   jan  => [qw/ ed hal gav abe bob jon col ian fred dan /],
 },

);

my %Engaged; my %Proposed;

match_them(); check_stability(); perturb(); check_stability();

sub match_them {

   say 'Matchmaking:';
   while(my $man = unmatched_man()) {
       my $woman = preferred_choice($man);
       $Proposed{$man}{$woman} = 1;
       if(! $Engaged{W}{$woman}) {
           engage($man, $woman);
           say "\t$woman and $man";
       }
       else {
           if(woman_prefers($woman, $man)) {
               my $engaged_man = $Engaged{W}{$woman};
               engage($man, $woman);
               undef $Engaged{M}{$engaged_man};
               say "\t$woman dumped $engaged_man for $man";
           }
       }
   }

}

sub check_stability {

   say 'Stablility:';
   my $stable = 1;
   foreach my $m (men()) {
       foreach my $w (women()) {
           if(man_prefers($m, $w) && woman_prefers($w, $m)) {
               say "\t$w prefers $m to $Engaged{W}{$w} and $m prefers $w to $Engaged{M}{$m}";
               $stable = 0;
           }
       }
   }
   if($stable) {
       say "\t(all marriages stable)";
   }

}

sub unmatched_man {

   return first { ! $Engaged{M}{$_} } men();

}

sub preferred_choice {

   my $man = shift;
   return first { ! $Proposed{$man}{$_} } @{ $Likes{M}{$man} };

}

sub engage {

   my ($man, $woman) = @_;
   $Engaged{W}{$woman} = $man;
   $Engaged{M}{$man} = $woman;

}

sub prefers {

   my $sex = shift;
   return sub {
       my ($person, $prospect) = @_;
       my $choices = join ' ', @{ $Likes{$sex}{$person} };
       return index($choices, $prospect) < index($choices, $Engaged{$sex}{$person});
   }

}

BEGIN {

   *woman_prefers = prefers('W');
   *man_prefers   = prefers('M');

}

sub perturb {

   say 'Perturb:';
   say "\tengage abi with fred and bea with jon";
   engage('fred' => 'abi');
   engage('jon'  => 'bea');

}

sub men { keys %{ $Likes{M} } } sub women { keys %{ $Likes{W} } }</lang>

Output:
Matchmaking:
        abi and abe
        ivy and dan
        abi dumped abe for jon
        eve and abe
        eve dumped abe for hal
        cath and abe
        gay and gav
        jan and ed
        hope and ian
        dee and col
        cath dumped abe for bob
        ivy dumped dan for abe
        fay and dan
        bea and fred
Stablility:
        (all marriages stable)
Perturb:
        engage abi with fred and bea with jon
Stablility:
        eve prefers jon to hal and jon prefers eve to bea
        gay prefers jon to gav and jon prefers gay to bea
        fay prefers jon to dan and jon prefers fay to bea
        bea prefers fred to jon and fred prefers bea to abi

Perl 6

Works with: rakudo version 2016.10
Translation of: Perl

<lang perl6>my %he-likes =

   abe  => < abi eve cath ivy jan dee fay bea hope gay >,
   bob  => < cath hope abi dee eve fay bea jan ivy gay >,
   col  => < hope eve abi dee bea fay ivy gay cath jan >,
   dan  => < ivy fay dee gay hope eve jan bea cath abi >,
   ed   => < jan dee bea cath fay eve abi ivy hope gay >,
   fred => < bea abi dee gay eve ivy cath jan hope fay >,
   gav  => < gay eve ivy bea cath abi dee hope jan fay >,
   hal  => < abi eve hope fay ivy cath jan bea gay dee >,
   ian  => < hope cath dee gay bea abi fay ivy jan eve >,
   jon  => < abi fay jan gay eve bea dee cath ivy hope >,

my %she-likes =

   abi  => < bob fred jon gav ian abe dan ed col hal >,
   bea  => < bob abe col fred gav dan ian ed jon hal >,
   cath => < fred bob ed gav hal col ian abe dan jon >,
   dee  => < fred jon col abe ian hal gav dan bob ed >,
   eve  => < jon hal fred dan abe gav col ed ian bob >,
   fay  => < bob abe ed ian jon dan fred gav col hal >,
   gay  => < jon gav hal fred bob abe col ed dan ian >,
   hope => < gav jon bob abe ian dan hal ed col fred >,
   ivy  => < ian col hal gav fred bob abe ed jon dan >,
   jan  => < ed hal gav abe bob jon col ian fred dan >,

my %fiancé; my %fiancée; my %proposed;

sub she-prefers ($her, $hottie) { .index($hottie) < .index(%fiancé{$her}) given ~%she-likes{$her} } sub he-prefers ($him, $hottie) { .index($hottie) < .index(%fiancée{$him}) given ~%he-likes{$him} }

match'em; check-stability;

perturb'em; check-stability;

sub match'em { #'

   say 'Matchmaking:';
   while unmatched-guy() -> $guy {
       my $gal = preferred-choice($guy);
       %proposed{"$guy $gal"} = '❤';
       if not %fiancé{$gal} {
           engage($guy, $gal);
           say "\t$gal and $guy";
       }
       elsif she-prefers($gal, $guy) {

my $engaged-guy = %fiancé{$gal}; engage($guy, $gal); %fiancée{$engaged-guy} = ; say "\t$gal dumped $engaged-guy for $guy"; }

   }

}

sub check-stability {

   my @instabilities = gather for flat %he-likes.keys X %she-likes.keys -> $m, $w {

if he-prefers($m, $w) and she-prefers($w, $m) { take "\t$w prefers $m to %fiancé{$w} and $m prefers $w to %fiancée{$m}"; }

   }
   say 'Stablility:';
   if @instabilities {

.say for @instabilities;

   }
   else {
       say "\t(all marriages stable)";
   }

}

sub unmatched-guy { %he-likes.keys.first: { not %fiancée{$_} } }

sub preferred-choice($guy) { %he-likes{$guy}.first: { not %proposed{"$guy $_" } } }

sub engage($guy, $gal) {

   %fiancé{$gal} = $guy;
   %fiancée{$guy} = $gal;

}

sub perturb'em { #'

   say 'Perturb:';
   say "\tengage abi with fred and bea with jon";
   engage('fred', 'abi');
   engage('jon', 'bea');

}</lang>

Output:
Matchmaking:
        cath and bob
        ivy and dan
        abi and jon
        hope and ian
        jan and ed
        eve and abe
        eve dumped abe for hal
        ivy dumped dan for abe
        fay and dan
        gay and gav
        bea and fred
        dee and col
Stablility:
        (all marriages stable)
Perturb:
        engage abi with fred and bea with jon
Stablility:
        fay prefers jon to dan and jon prefers fay to bea
        eve prefers jon to hal and jon prefers eve to bea
        gay prefers jon to gav and jon prefers gay to bea
        bea prefers fred to jon and fred prefers bea to abi

PicoLisp

<lang PicoLisp>(setq

  *Boys (list
     (de abe  abi eve cath ivy jan dee fay bea hope gay)
     (de bob  cath hope abi dee eve fay bea jan ivy gay)
     (de col  hope eve abi dee bea fay ivy gay cath jan)
     (de dan  ivy fay dee gay hope eve jan bea cath abi)
     (de ed   jan dee bea cath fay eve abi ivy hope gay)
     (de fred bea abi dee gay eve ivy cath jan hope fay)
     (de gav  gay eve ivy bea cath abi dee hope jan fay)
     (de hal  abi eve hope fay ivy cath jan bea gay dee)
     (de ian  hope cath dee gay bea abi fay ivy jan eve)
     (de jon  abi fay jan gay eve bea dee cath ivy hope) )
  *Girls (list
     (de bi   bob fred jon gav ian abe dan ed col hal)
     (de bea  bob abe col fred gav dan ian ed jon hal)
     (de cath fred bob ed gav hal col ian abe dan jon)
     (de dee  fred jon col abe ian hal gav dan bob ed)
     (de eve  jon hal fred dan abe gav col ed ian bob)
     (de fay  bob abe ed ian jon dan fred gav col hal)
     (de gay  jon gav hal fred bob abe col ed dan ian)
     (de hope gav jon bob abe ian dan hal ed col fred)
     (de ivy  ian col hal gav fred bob abe ed jon dan)
     (de jan  ed hal gav abe bob jon col ian fred dan) )
  *Couples NIL )

(bind *Boys

  (while
     (find
        '((Boy) (and (val Boy) (not (asoq Boy *Couples))))
        *Boys )
     (let (Boy @  Girl (pop Boy)  Pair (find '((P) (== Girl (cdr P))) *Couples))
        (nond
           (Pair (push '*Couples (cons Boy Girl)))   # Girl is free
           ((memq Boy (memq (car Pair) (val Girl)))  # Girl prefers Boy
              (set Pair Boy) ) ) ) ) )

(for Pair *Couples

  (prinl (cdr Pair) " is engaged to " (car Pair)) )

(de checkCouples ()

  (unless
     (filter
        '((Pair)
           (let (Boy (car Pair)  Girl (cdr Pair))
              (find
                 '((B)
                    (and
                       (memq Boy (cdr (memq B (val Girl))))  # Girl prefers B
                       (memq
                          (cdr (asoq B *Couples))            # and B prefers Girl
                          (cdr (memq Girl (val B))) )
                       (prinl
                          Girl " likes " B " better than " Boy " and "
                          B " likes " Girl " better than "
                          (cdr (asoq B *Couples)) ) ) )
                 (val Girl) ) ) )
        *Couples )
     (prinl "All marriages are stable") ) )

(checkCouples) (prinl) (prinl "Engage fred with abi and jon with bea") (con (asoq 'fred *Couples) 'abi) (con (asoq 'jon *Couples) 'bea) (checkCouples)</lang>

Output:
dee is engaged to col
fay is engaged to dan
eve is engaged to hal
gay is engaged to gav
bea is engaged to fred
jan is engaged to ed
ivy is engaged to abe
hope is engaged to ian
cath is engaged to bob
abi is engaged to jon
All marriages are stable

Engage fred with abi and jon with bea
fay likes jon better than dan and jon likes fay better than bea
eve likes jon better than hal and jon likes eve better than bea
gay likes jon better than gav and jon likes gay better than bea
bea likes fred better than jon and fred likes bea better than abi

Prolog

Works with: SWI-Prolog
Library: XPCE

XPCE is used for its integrated messaging system. <lang Prolog>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % facts prefere(abe,[ abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay]). prefere( bob,[ cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay]). prefere( col,[ hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan]). prefere( dan,[ ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi]). prefere( ed,[ jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay]). prefere( fred,[ bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay]). prefere( gav,[ gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay]). prefere( hal,[ abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee]). prefere( ian,[ hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve]). prefere( jon,[ abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope]).

prefere( abi,[ bob, fred, jon, gav, ian, abe, dan, ed, col, hal]). prefere( bea,[ bob, abe, col, fred, gav, dan, ian, ed, jon, hal]). prefere( cath,[ fred, bob, ed, gav, hal, col, ian, abe, dan, jon]). prefere( dee,[ fred, jon, col, abe, ian, hal, gav, dan, bob, ed]). prefere( eve,[ jon, hal, fred, dan, abe, gav, col, ed, ian, bob]). prefere( fay,[ bob, abe, ed, ian, jon, dan, fred, gav, col, hal]). prefere( gay,[ jon, gav, hal, fred, bob, abe, col, ed, dan, ian]). prefere( hope,[ gav, jon, bob, abe, ian, dan, hal, ed, col, fred]). prefere( ivy,[ ian, col, hal, gav, fred, bob, abe, ed, jon, dan]). prefere( jan,[ ed, hal, gav, abe, bob, jon, col, ian, fred, dan]).


man(abe). man(bob). man(col). man(dan). man(ed). man(fred). man(gav). man(hal). man(ian). man(jon).

woman(abi). woman(bea). woman(cath). woman(dee). woman(eve). woman(fay). woman(gay). woman(hope). woman(ivy). woman(jan).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % rules

stable_mariage :- new(LstMan, chain), forall(man(X), ( prefere(X, Lst), new(P, man(X, Lst)), send(LstMan, append, P))),

new(LstWoman, chain), forall(woman(X), ( prefere(X, Lst), new(P, woman(X, Lst)), send(LstWoman, append, P))), send(LstMan, for_all, message(@arg1, init_liste, LstWoman)), send(LstWoman, for_all, message(@arg1, init_liste, LstMan)),

round(LstMan, LstWoman), new(LstCouple, chain), % creation of the couple. send(LstWoman, for_all, and(message(@prolog, create_couple, @arg1, LstCouple), message(@pce, write_ln, @arg1?name, with, @arg1?elu?name))),

nl,

% test of the stability of couples stability(LstCouple), nl,

% Perturbation of couples get(LstCouple, size, Len), get_two_random_couples(Len, V1, V2),

get(LstCouple, nth0, V1, C1), get(LstCouple, nth0, V2, C2), new(NC1, tuple(C1?first, C2?second)), new(NC2, tuple(C2?first, C1?second)), send(LstCouple, nth0, V1, NC1), send(LstCouple, nth0, V2, NC2),

send(@pce, write_ln, 'perturbation of couples'), send(@pce, write_ln, NC1?second, with, NC1?first), send(@pce, write_ln, NC2?second, with, NC2?first), nl,

stability(LstCouple).

get_two_random_couples(Len, C1, C2) :- C1 is random(Len), repeat, C2 is random(Len), C1 \= C2.

create_couple(Woman, LstCouple ) :- send(LstCouple, append, new(_, tuple(Woman?elu?name, Woman?name))).

% iterations of the algorithm round(LstMan, LstWoman) :- send(LstMan, for_some, message(@arg1, propose)), send(LstWoman, for_some, message(@arg1, dispose)), ( \+send(LstWoman, for_all, @arg1?status == maybe) -> round(LstMan, LstWoman) ; true ).

-pce_begin_class(person, object, "description of a person").

variable(name, object, both, "name of the person"). variable(preference, chain, both, "list of priority"). variable(status, object, both, "statut of engagement : maybe / free").

initialise(P, Name, Pref) :-> send(P, send_super, initialise), send(P, slot, name, Name), send(P, slot, preference, Pref), send(P, slot, status, free).

% reception of the list of partners init_liste(P, Lst) :-> % we replace the list of name of partners % with the list of persons partners. new(NLP, chain), get(P, slot, preference, LP), send(LP, for_all, message(@prolog, find_person,@arg1, Lst, NLP)), send(P, slot, preference, NLP).

- pce_end_class(person).


find_person(Name, LstPerson, LstPref) :- get(LstPerson, find, @arg1?name == Name, Elem), send(LstPref, append, Elem).

-pce_begin_class(man, person, "description of a man").

initialise(P, Name, Pref) :-> send(P, send_super, initialise, Name, Pref).

% a man propose "la botte" to a woman propose(P) :-> get(P, slot, status, free), get(P, slot, preference, XPref), get(XPref, delete_head, Pref), send(P, slot, preference, XPref), send(Pref, proposition, P).

refuse(P) :-> send(P, slot, status, free).

accept(P) :-> send(P, slot, status, maybe).

- pce_end_class(man).
-pce_begin_class(woman, person, "description of a woman").

variable(elu, object, both, "name of the elu"). variable(contact, chain, both, "men that have contact this woman").

initialise(P, Name, Pref) :-> send(P, send_super, initialise, Name, Pref), send(P, slot, contact, new(_, chain)), send(P, slot, elu, @nil).

% a woman decide Maybe/No dispose(P) :-> get(P, slot, contact, Contact), get(P, slot, elu, Elu),

( Elu \= @nil -> send(Contact, append, Elu) ; true),

new(R, chain), send(Contact, for_all, message(P, fetch, @arg1, R)), send(R, sort, ?(@arg1?first, compare, @arg2?first)), get(R, delete_head, Tete), send(Tete?second, accept), send(P, slot, status, maybe), send(P, slot, elu, Tete?second), send(R, for_some, message(@arg1?second, refuse)), send(P, slot, contact, new(_, chain)) .


% looking for the person of the given name Contact % Adding it in the chain Chain fetch(P, Contact, Chain) :-> get(P, slot, preference, Lst), get(Lst, find, @arg1?name == Contact?name, Elem), get(Lst, index, Elem, Ind), send(Chain, append, new(_, tuple(Ind, Contact))).

% a woman receive a proposition from a man proposition(P, Name) :-> get(P, slot, contact, C), send(C, append, Name), send(P, slot, contact, C).

- pce_end_class(woman).

% computation of the stability od couple stability(LstCouple) :- chain_list(LstCouple, LstPceCouple), maplist(transform, LstPceCouple, PrologLstCouple), study_couples(PrologLstCouple, [], UnstableCouple), ( UnstableCouple = [] -> writeln('Couples are stable') ; sort(UnstableCouple, SortUnstableCouple), writeln('Unstable couples are'), maplist(print_unstable_couple, SortUnstableCouple), nl ).


print_unstable_couple((C1, C2)) :- format('~w and ~w~n', [C1, C2]).

transform(PceCouple, couple(First, Second)):- get(PceCouple?first, value, First), get(PceCouple?second, value, Second).

study_couples([], UnstableCouple, UnstableCouple).

study_couples([H | T], CurrentUnstableCouple, UnstableCouple):- include(unstable_couple(H), T, Lst), ( Lst \= [] -> maplist(build_one_couple(H), Lst, Lst1), append(CurrentUnstableCouple, Lst1,CurrentUnstableCouple1) ; CurrentUnstableCouple1 = CurrentUnstableCouple ), study_couples(T, CurrentUnstableCouple1, UnstableCouple).


build_one_couple(C1, C2, (C1, C2)).

unstable_couple(couple(X1, Y1), couple(X2, Y2)) :- prefere(X1, PX1), prefere(X2, PX2), prefere(Y1, PY1), prefere(Y2, PY2),

% index of women for X1 nth0(IY12, PX1, Y2), nth0(IY11, PX1, Y1), % index of men for Y2 nth0(IX21, PY2, X1), nth0(IX22, PY2, X2),

% index of women for X2 nth0(IY21, PX2, Y1), nth0(IY22, PX2, Y2), % index of men for Y1 nth0(IX11, PY1, X1), nth0(IX12, PY1, X2),

% A couple is unstable ( (IY12 < IY11 , IX21 < IX22); (IY21 < IY22 , IX12 < IX11)). </lang>

Output:
 ?- stable_mariage.
abi with jon
bea with fred
cath with bob
dee with col
eve with hal
fay with dan
gay with gav
hope with ian
ivy with abe
jan with ed

Couples are stable

perturbation of couples
gay with jon
abi with gav

Unstable couples are
couple(gav,abi) and couple(abe,ivy)
couple(jon,gay) and couple(dan,fay)
couple(jon,gay) and couple(gav,abi)

true 

A more Prolog-ish version (working with SWI-Prolog) could be : <lang Prolog>:- dynamic person/4, prop/2. % person(Name, Preference, Status, Candidate) % prop(Name, List_of_Candidates) (for a woman)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % facts prefere(abe,[ abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay]). prefere( bob,[ cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay]). prefere( col,[ hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan]). prefere( dan,[ ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi]). prefere( ed,[ jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay]). prefere( fred,[ bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay]). prefere( gav,[ gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay]). prefere( hal,[ abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee]). prefere( ian,[ hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve]). prefere( jon,[ abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope]).

prefere( abi,[ bob, fred, jon, gav, ian, abe, dan, ed, col, hal]). prefere( bea,[ bob, abe, col, fred, gav, dan, ian, ed, jon, hal]). prefere( cath,[ fred, bob, ed, gav, hal, col, ian, abe, dan, jon]). prefere( dee,[ fred, jon, col, abe, ian, hal, gav, dan, bob, ed]). prefere( eve,[ jon, hal, fred, dan, abe, gav, col, ed, ian, bob]). prefere( fay,[ bob, abe, ed, ian, jon, dan, fred, gav, col, hal]). prefere( gay,[ jon, gav, hal, fred, bob, abe, col, ed, dan, ian]). prefere( hope,[ gav, jon, bob, abe, ian, dan, hal, ed, col, fred]). prefere( ivy,[ ian, col, hal, gav, fred, bob, abe, ed, jon, dan]). prefere( jan,[ ed, hal, gav, abe, bob, jon, col, ian, fred, dan]).


man(abe). man(bob). man(col). man(dan). man(ed). man(fred). man(gav). man(hal). man(ian). man(jon).

woman(abi). woman(bea). woman(cath). woman(dee). woman(eve). woman(fay). woman(gay). woman(hope). woman(ivy). woman(jan).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % rules stable_mariage :- %initialization retractall(person(_,_,_,_)), retractall(prop(_,_)), forall(prefere(P, Pref), assert(person(P, Pref, free, none))), bagof(X, man(X), LstMen), bagof(Y, woman(Y), LstWomen), forall(member(Z, LstWomen), assert(prop(Z, []))),

% compute the mariages iteration(LstMen, LstWomen, LstCouple), maplist(print_couple,LstCouple), nl,

% test of the stability of couples stability(LstCouple), nl,

% Perturbation of couples length(LstCouple, Len), get_two_random_couples(Len, V1, V2),

nth0(V1, LstCouple, C1), select(C1, LstCouple, Lst1), ( V2 > 0 -> V22 is V2 - 1; V22 = V2), nth0(V22, Lst1, C2), select(C2, Lst1, Lst2), C1 = couple(M1, W1), C2 = couple(M2, W2),

writeln('perturbation of couples'), format('~w with ~w~n', [W1, M2]), format('~w with ~w~n', [W2, M1]), nl, stability([couple(M1, W2), couple(M2, W1)| Lst2]).


% the algorithm iteration(Men, Women, LstCouples) :- % Men propose bagof(M, X^Y^(member(M, Men),person(M, X, free, Y)), LM), forall(member(X, LM), ( retract(person(X, [W|Pref], free, Elu)), assert(person(X, Pref, free, Elu)), retract(prop(W, Prop)), assert(prop(W, [X| Prop])))),

% women dispose bagof(W, L^(prop(W, L), L \= []), LW), forall(member(W, LW), ( retract(prop(W, Prop)), retract(person(W, Pref, _, Elu)), ( Elu = none -> Prop1 = Prop; Prop1 = [Elu|Prop]), order_prop(Pref, Prop1, [M | Prop2]), retract(person(M, PrefM, _, _)), assert(person(M, PrefM, maybe, W)), forall(member(Y, Prop2), ( retract(person(Y, Pref1, _, _TE)), assert(person(Y, Pref1, free, none)))), assert(prop(W, [])), assert(person(W, Pref, maybe, M)) )),

% finished ? ( bagof(X, T^Z^(member(X, Women), person(X, T, free, Z)), _LW1) -> iteration(Men, Women, LstCouples) ; make_couple(Women, LstCouples) ).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % compute order preference of candidates. order_prop(Pref, Prop, Res) :- maplist(index(Pref), Prop, Rtemp), sort(Rtemp, Rtemp1), maplist(simplifie,Rtemp1, Res).

index(Lst, Value, [Ind, Value]) :- nth0(Ind, Lst, Value).

simplifie([_, V], V).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% print_couple(couple(M, W)) :- format('~w with ~w~n', [W, M]).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % creation of couples make_couple([], []).

make_couple([W | LW], [couple(M, W) | LC]) :- make_couple(LW, LC), person(W, _, _, M).

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % miscellaneous get_two_random_couples(Len, C1, C2) :- C1 is random(Len), repeat, C2 is random(Len), C1 \= C2.

print_unstable_couple((C1, C2)) :- format('~w and ~w~n', [C1, C2]).


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % test the stability of couples stability(LstCouple) :- study_couples(LstCouple, [], CoupleInstable), ( CoupleInstable = [] -> writeln('Couples are stable') ; sort(CoupleInstable, SortCoupleInstable), writeln('Unstable couples are'), maplist(print_unstable_couple, SortCoupleInstable), nl ).


% compute the stability od couple study_couples([], UnstableCouple, UnstableCouple).

study_couples([H | T], CurrentUnstableCouple, UnstableCouple):- include(unstable_couple(H), T, Lst), ( Lst \= [] -> maplist(build_one_couple(H), Lst, Lst1), append(CurrentUnstableCouple, Lst1,CurrentUnstableCouple1) ; CurrentUnstableCouple1 = CurrentUnstableCouple ), study_couples(T, CurrentUnstableCouple1, UnstableCouple).


build_one_couple(C1, C2, (C1, C2)).

unstable_couple(couple(X1, Y1), couple(X2, Y2)) :- prefere(X1, PX1), prefere(X2, PX2), prefere(Y1, PY1), prefere(Y2, PY2),

% index of women for X1 nth0(IY12, PX1, Y2), nth0(IY11, PX1, Y1), % index of men for Y2 nth0(IX21, PY2, X1), nth0(IX22, PY2, X2),

% index of women for X2 nth0(IY21, PX2, Y1), nth0(IY22, PX2, Y2), % index of men for Y1 nth0(IX11, PY1, X1), nth0(IX12, PY1, X2),

% A couple is unstable ( (IY12 < IY11 , IX21 < IX22); (IY21 < IY22 , IX12 < IX11)).</lang>

PureBasic

This approach uses a messaging system to pass messages between prospective partners. <lang PureBasic>#coupleCount = 10

DataSection

 ;guys
 Data.s "abe: abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay"
 Data.s "bob: cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay"
 Data.s "col: hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan"
 Data.s "dan: ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi"
 Data.s "ed: jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay"
 Data.s "fred: bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay"
 Data.s "gav: gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay"
 Data.s "hal: abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee"
 Data.s "ian: hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve"
 Data.s "jon: abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope"
 ;gals
 Data.s "abi: bob, fred, jon, gav, ian, abe, dan, ed, col, hal"
 Data.s "bea: bob, abe, col, fred, gav, dan, ian, ed, jon, hal"
 Data.s "cath: fred, bob, ed, gav, hal, col, ian, abe, dan, jon"
 Data.s "dee: fred, jon, col, abe, ian, hal, gav, dan, bob, ed"
 Data.s "eve: jon, hal, fred, dan, abe, gav, col, ed, ian, bob"
 Data.s "fay: bob, abe, ed, ian, jon, dan, fred, gav, col, hal"
 Data.s "gay: jon, gav, hal, fred, bob, abe, col, ed, dan, ian"
 Data.s "hope: gav, jon, bob, abe, ian, dan, hal, ed, col, fred"
 Data.s "ivy: ian, col, hal, gav, fred, bob, abe, ed, jon, dan"
 Data.s "jan: ed, hal, gav, abe, bob, jon, col, ian, fred, dan"

EndDataSection

Structure message

 source.s ;person that message is from
 dest.s   ;person that message is for
 action.s ;{'P', 'A', 'D', 'B'} for proposal, accept, decline, break-up

EndStructure

Structure person

 name.s
 isEngagedTo.s
 List prefs.s()

EndStructure

Global NewList messages.message()

Procedure setupPersons(List persons.person(), count)

 Protected i, j, start, pref$
 For i = 1 To count
   Read.s pref$
   pref$ = LCase(pref$)
   start = FindString(pref$, ":", 1)
   AddElement(persons())
   persons()\name = Left(pref$, start - 1)
   pref$ = Trim(Right(pref$, Len(pref$) - start))
   For j = 1 To count
     AddElement(persons()\prefs())
     persons()\prefs() = Trim(StringField(pref$, j, ","))
   Next
 Next

EndProcedure

Procedure sendMessage(source.s, dest.s, action.s)

 LastElement(messages())
 AddElement(messages())
 With messages()
   \source = source
   \dest = dest
   \action = action
 EndWith
 ResetList(messages())

EndProcedure

Procedure selectPerson(name.s, List persons.person())

 ForEach persons()
   If persons()\name = name
     Break
   EndIf 
 Next 

EndProcedure

Procedure rankPerson(name.s, List prefs.s())

 ForEach prefs()
   If prefs() = name
     ProcedureReturn #coupleCount - ListIndex(prefs()) ;higher is better
   EndIf 
 Next 
 ProcedureReturn -1 ;no rank, shouldn't occur

EndProcedure

Procedure stabilityCheck(List guys.person(), List gals.person())

 Protected isStable = #True
 ForEach guys()
   rankPerson(guys()\isEngagedTo, guys()\prefs())
   While PreviousElement(guys()\prefs())
     selectPerson(guys()\prefs(), gals())
     If rankPerson(guys()\name, gals()\prefs()) > rankPerson(gals()\isEngagedTo, gals()\prefs())
       Print("  " + gals()\name + " loves " + guys()\name + " more than " + gals()\isEngagedTo + ",")
       PrintN(" And " + guys()\name + " loves " + gals()\name + " more than " + guys()\isEngagedTo + ".")
       isStable = #False
     EndIf
   Wend 
 Next
 If isStable
   PrintN(#CRLF$ + "Marriage stability check PASSED.")
 Else 
   PrintN(#CRLF$ + "Marriage stability check FAILED.")
 EndIf

EndProcedure

NewList guys.person() NewList gals.person() setupPersons(guys(), #coupleCount) setupPersons(gals(), #coupleCount)

make initial round of proposals

ForEach guys()

 FirstElement(guys()\prefs())
 sendMessage(guys()\name, guys()\prefs(), "P")

Next

dispatch messages

Define source.s, dest.s, action.s ForEach messages()

 source = messages()\source
 dest = messages()\dest
 action = messages()\action
 
 DeleteElement(messages())
 Select action
   Case "P" ;propose ;only message received by gals
     selectPerson(dest, gals())
     selectPerson(source, guys())
     If rankPerson(guys()\name, gals()\prefs()) < rankPerson(gals()\isEngagedTo, gals()\prefs())
       sendMessage(dest, source, "D") ;decline proposal
     ElseIf rankPerson(guys()\name, gals()\prefs()) > rankPerson(gals()\isEngagedTo, gals()\prefs())
       If gals()\isEngagedTo
         sendMessage(dest, gals()\isEngagedTo, "B")  ;break-up engagement
       EndIf 
       gals()\isEngagedTo = source
       sendMessage(dest, source, "A") ;accept proposal
     EndIf 
   Case "A", "D", "B" ;messages received by guys
     selectPerson(dest, guys())
     If action = "A" ;proposal accepted
       guys()\isEngagedTo = source 
     Else
       If action = "B" ;broke-up
         guys()\isEngagedTo = ""
       EndIf 
       NextElement(guys()\prefs())
       sendMessage(dest, guys()\prefs(),"P") ;propose to next pref
     EndIf  
 EndSelect

Next

If OpenConsole()

 PrintN("Marriages:")
 ForEach guys()
   PrintN("  " + guys()\name + " And " + guys()\isEngagedTo + ".")
 Next
 stabilityCheck(guys(), gals())
 Define *person_1.person, *person_2.person
 PrintN(#CRLF$ + "Introducing an error by swapping partners of abi and bea.")
 selectPerson("abi", gals()): *person_1 = @gals()
 selectPerson("bea", gals()): *person_2 = @gals()
 Swap *person_1\isEngagedTo, *person_2\isEngagedTo
 selectPerson(*person_1\isEngagedTo, guys()): *person_1 = @guys()
 selectPerson(*person_1\isEngagedTo, guys()): *person_2 = @guys()
 Swap *person_1\isEngagedTo, *person_2\isEngagedTo
 PrintN("  " + *person_1\name + " is now with " + *person_1\isEngagedTo + ".")
 PrintN("  " + *person_2\name + " is now with " + *person_2\isEngagedTo + ".")
 PrintN("")
 stabilityCheck(guys(), gals())
 
 Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input()
 CloseConsole()

EndIf</lang>

Output:
Marriages:
  abe And ivy.
  bob And cath.
  col And dee.
  dan And fay.
  ed And jan.
  fred And bea.
  gav And gay.
  hal And eve.
  ian And hope.
  jon And abi.

Marriage stability check PASSED.

Introducing an error by swapping partners of abi and bea.
  fred is now with abi.
  jon is now with bea.

  bea loves fred more than jon, And fred loves bea more than abi.
  eve loves jon more than hal, And jon loves eve more than bea.
  gay loves jon more than gav, And jon loves gay more than bea.
  fay loves jon more than dan, And jon loves fay more than bea.

Marriage stability check FAILED.

Python

<lang python>import copy

guyprefers = {

'abe':  ['abi', 'eve', 'cath', 'ivy', 'jan', 'dee', 'fay', 'bea', 'hope', 'gay'],
'bob':  ['cath', 'hope', 'abi', 'dee', 'eve', 'fay', 'bea', 'jan', 'ivy', 'gay'],
'col':  ['hope', 'eve', 'abi', 'dee', 'bea', 'fay', 'ivy', 'gay', 'cath', 'jan'],
'dan':  ['ivy', 'fay', 'dee', 'gay', 'hope', 'eve', 'jan', 'bea', 'cath', 'abi'],
'ed':   ['jan', 'dee', 'bea', 'cath', 'fay', 'eve', 'abi', 'ivy', 'hope', 'gay'],
'fred': ['bea', 'abi', 'dee', 'gay', 'eve', 'ivy', 'cath', 'jan', 'hope', 'fay'],
'gav':  ['gay', 'eve', 'ivy', 'bea', 'cath', 'abi', 'dee', 'hope', 'jan', 'fay'],
'hal':  ['abi', 'eve', 'hope', 'fay', 'ivy', 'cath', 'jan', 'bea', 'gay', 'dee'],
'ian':  ['hope', 'cath', 'dee', 'gay', 'bea', 'abi', 'fay', 'ivy', 'jan', 'eve'],
'jon':  ['abi', 'fay', 'jan', 'gay', 'eve', 'bea', 'dee', 'cath', 'ivy', 'hope']}

galprefers = {

'abi':  ['bob', 'fred', 'jon', 'gav', 'ian', 'abe', 'dan', 'ed', 'col', 'hal'],
'bea':  ['bob', 'abe', 'col', 'fred', 'gav', 'dan', 'ian', 'ed', 'jon', 'hal'],
'cath': ['fred', 'bob', 'ed', 'gav', 'hal', 'col', 'ian', 'abe', 'dan', 'jon'],
'dee':  ['fred', 'jon', 'col', 'abe', 'ian', 'hal', 'gav', 'dan', 'bob', 'ed'],
'eve':  ['jon', 'hal', 'fred', 'dan', 'abe', 'gav', 'col', 'ed', 'ian', 'bob'],
'fay':  ['bob', 'abe', 'ed', 'ian', 'jon', 'dan', 'fred', 'gav', 'col', 'hal'],
'gay':  ['jon', 'gav', 'hal', 'fred', 'bob', 'abe', 'col', 'ed', 'dan', 'ian'],
'hope': ['gav', 'jon', 'bob', 'abe', 'ian', 'dan', 'hal', 'ed', 'col', 'fred'],
'ivy':  ['ian', 'col', 'hal', 'gav', 'fred', 'bob', 'abe', 'ed', 'jon', 'dan'],
'jan':  ['ed', 'hal', 'gav', 'abe', 'bob', 'jon', 'col', 'ian', 'fred', 'dan']}

guys = sorted(guyprefers.keys()) gals = sorted(galprefers.keys())


def check(engaged):

   inverseengaged = dict((v,k) for k,v in engaged.items())
   for she, he in engaged.items():
       shelikes = galprefers[she]
       shelikesbetter = shelikes[:shelikes.index(he)]
       helikes = guyprefers[he]
       helikesbetter = helikes[:helikes.index(she)]
       for guy in shelikesbetter:
           guysgirl = inverseengaged[guy]
           guylikes = guyprefers[guy]
           if guylikes.index(guysgirl) > guylikes.index(she):
               print("%s and %s like each other better than "
                     "their present partners: %s and %s, respectively"
                     % (she, guy, he, guysgirl))
               return False
       for gal in helikesbetter:
           girlsguy = engaged[gal]
           gallikes = galprefers[gal]
           if gallikes.index(girlsguy) > gallikes.index(he):
               print("%s and %s like each other better than "
                     "their present partners: %s and %s, respectively"
                     % (he, gal, she, girlsguy))
               return False
   return True

def matchmaker():

   guysfree = guys[:]
   engaged  = {}
   guyprefers2 = copy.deepcopy(guyprefers)
   galprefers2 = copy.deepcopy(galprefers)
   while guysfree:
       guy = guysfree.pop(0)
       guyslist = guyprefers2[guy]
       gal = guyslist.pop(0)
       fiance = engaged.get(gal)
       if not fiance:
           # She's free
           engaged[gal] = guy
           print("  %s and %s" % (guy, gal))
       else:
           # The bounder proposes to an engaged lass!
           galslist = galprefers2[gal]
           if galslist.index(fiance) > galslist.index(guy):
               # She prefers new guy
               engaged[gal] = guy
               print("  %s dumped %s for %s" % (gal, fiance, guy))
               if guyprefers2[fiance]:
                   # Ex has more girls to try
                   guysfree.append(fiance)
           else:
               # She is faithful to old fiance
               if guyslist:
                   # Look again
                   guysfree.append(guy)
   return engaged


print('\nEngagements:') engaged = matchmaker()

print('\nCouples:') print(' ' + ',\n '.join('%s is engaged to %s' % couple

                         for couple in sorted(engaged.items())))

print() print('Engagement stability check PASSED'

     if check(engaged) else 'Engagement stability check FAILED')

print('\n\nSwapping two fiances to introduce an error') engaged[gals[0]], engaged[gals[1]] = engaged[gals[1]], engaged[gals[0]] for gal in gals[:2]:

   print('  %s is now engaged to %s' % (gal, engaged[gal]))

print() print('Engagement stability check PASSED'

     if check(engaged) else 'Engagement stability check FAILED')</lang>
Output:
Engagements:
  abe and abi
  bob and cath
  col and hope
  dan and ivy
  ed and jan
  fred and bea
  gav and gay
  hope dumped col for ian
  abi dumped abe for jon
  hal and eve
  col and dee
  ivy dumped dan for abe
  dan and fay

Couples:
  abi is engaged to jon,
  bea is engaged to fred,
  cath is engaged to bob,
  dee is engaged to col,
  eve is engaged to hal,
  fay is engaged to dan,
  gay is engaged to gav,
  hope is engaged to ian,
  ivy is engaged to abe,
  jan is engaged to ed

Engagement stability check PASSED


Swapping two fiances to introduce an error
  abi is now engaged to fred
  bea is now engaged to jon

fay and jon like each other better than their present partners: dan and bea, respectively
Engagement stability check FAILED

Ruby

<lang ruby>class Person

 def initialize(name)
   @name = name
   @fiance = nil
   @preferences = []
   @proposals = []
 end
 attr_reader :name, :proposals
 attr_accessor :fiance, :preferences
 def to_s
   @name
 end
 def free
   @fiance = nil
 end
 def single?
   @fiance == nil
 end
 def engage(person)
   self.fiance = person
   person.fiance = self
 end
 def better_choice?(person)
   @preferences.index(person) < @preferences.index(@fiance)
 end
 def propose_to(person)
   puts "#{self} proposes to #{person}" if $DEBUG
   @proposals << person
   person.respond_to_proposal_from(self)
 end
 def respond_to_proposal_from(person)
   if single?
     puts "#{self} accepts proposal from #{person}" if $DEBUG
     engage(person)
   elsif better_choice?(person)
     puts "#{self} dumps #{@fiance} for #{person}" if $DEBUG
     @fiance.free
     engage(person)
   else
     puts "#{self} rejects proposal from #{person}" if $DEBUG
   end
 end

end

  1. initialize data

prefs = {

 'abe'  => %w[abi eve cath ivy jan dee fay bea hope gay],
 'bob'  => %w[cath hope abi dee eve fay bea jan ivy gay],
 'col'  => %w[hope eve abi dee bea fay ivy gay cath jan],
 'dan'  => %w[ivy fay dee gay hope eve jan bea cath abi],
 'ed'   => %w[jan dee bea cath fay eve abi ivy hope gay],
 'fred' => %w[bea abi dee gay eve ivy cath jan hope fay],
 'gav'  => %w[gay eve ivy bea cath abi dee hope jan fay],
 'hal'  => %w[abi eve hope fay ivy cath jan bea gay dee],
 'ian'  => %w[hope cath dee gay bea abi fay ivy jan eve],
 'jon'  => %w[abi fay jan gay eve bea dee cath ivy hope],
 'abi'  => %w[bob fred jon gav ian abe dan ed col hal],
 'bea'  => %w[bob abe col fred gav dan ian ed jon hal],
 'cath' => %w[fred bob ed gav hal col ian abe dan jon],
 'dee'  => %w[fred jon col abe ian hal gav dan bob ed],
 'eve'  => %w[jon hal fred dan abe gav col ed ian bob],
 'fay'  => %w[bob abe ed ian jon dan fred gav col hal],
 'gay'  => %w[jon gav hal fred bob abe col ed dan ian],
 'hope' => %w[gav jon bob abe ian dan hal ed col fred],
 'ivy'  => %w[ian col hal gav fred bob abe ed jon dan],
 'jan'  => %w[ed hal gav abe bob jon col ian fred dan],

}

@men = Hash[

 %w[abe bob col dan ed fred gav hal ian jon].collect do |name|
   [name, Person.new(name)]
 end

]

@women = Hash[

 %w[abi bea cath dee eve fay gay hope ivy jan].collect do |name|
   [name, Person.new(name)]
 end

]

@men.each {|name, man| man.preferences = @women.values_at(*prefs[name])} @women.each {|name, woman| woman.preferences = @men.values_at(*prefs[name])}

  1. perform the matching

def match_couples(men, women)

 men.each_value {|man| man.free}
 women.each_value {|woman| woman.free}
 while m = men.values.find {|man| man.single?} do
   puts "considering single man #{m}" if $DEBUG
   w = m.preferences.find {|woman| not m.proposals.include?(woman)}
   m.propose_to(w)
 end

end

match_couples @men, @women

@men.each_value.collect {|man| puts "#{man} + #{man.fiance}"}

  1. check for stability

class Person

 def more_preferable_people
   ( @preferences.partition {|p| better_choice?(p)} ).first
 end

end

require 'set'

def stability(men)

 unstable = Set.new
 men.each_value do |man|
   woman = man.fiance
   puts "considering #{man} and #{woman}" if $DEBUG
   man.more_preferable_people.each do |other_woman|
     if other_woman.more_preferable_people.include?(man)
       puts "an unstable pairing: #{man} and #{other_woman}" if $DEBUG
       unstable << [man, other_woman]
     end
   end
   woman.more_preferable_people.each do |other_man|
     if other_man.more_preferable_people.include?(woman)
       puts "an unstable pairing: #{woman} and #{other_man}" if $DEBUG
       unstable << [other_man, woman]
     end
   end
 end
 if unstable.empty?
   puts "these couples are stable"
 else
   puts "uh oh"
   unstable.each do |a,b|
     puts "#{a} is engaged to #{a.fiance} but would prefer #{b}, and #{b} is engaged to #{b.fiance} but would prefer #{a}"
   end
 end

end

stability @men

  1. perturb

puts "\nwhat if abe and bob swap..."

def swap(m1, m2)

 w1 = m1.fiance
 w2 = m2.fiance
 m1.fiance = w2
 w1.fiance = m2
 m2.fiance = w1
 w2.fiance = m1

end

swap *@men.values_at('abe','bob')

@men.each_value.collect {|man| puts "#{man} + #{man.fiance}"} stability @men</lang>

Output:
abe + ivy
bob + cath
col + dee
dan + fay
ed + jan
fred + bea
gav + gay
hal + eve
ian + hope
jon + abi
these couples are stable

what if abe and bob swap...
abe + cath
bob + ivy
col + dee
dan + fay
ed + jan
fred + bea
gav + gay
hal + eve
ian + hope
jon + abi
uh oh
bob is engaged to ivy but would prefer cath, and cath is engaged to abe but would prefer bob
bob is engaged to ivy but would prefer hope, and hope is engaged to ian but would prefer bob
bob is engaged to ivy but would prefer abi, and abi is engaged to jon but would prefer bob
bob is engaged to ivy but would prefer fay, and fay is engaged to dan but would prefer bob
bob is engaged to ivy but would prefer bea, and bea is engaged to fred but would prefer bob

Hmm, turns out Bob is a popular guy...

Racket

<lang Racket>

  1. lang racket

(define MEN

 '([abe  abi  eve  cath ivy  jan  dee  fay  bea  hope gay ]
   [bob  cath hope abi  dee  eve  fay  bea  jan  ivy  gay ]
   [col  hope eve  abi  dee  bea  fay  ivy  gay  cath jan ]
   [dan  ivy  fay  dee  gay  hope eve  jan  bea  cath abi ]
   [ed   jan  dee  bea  cath fay  eve  abi  ivy  hope gay ]
   [fred bea  abi  dee  gay  eve  ivy  cath jan  hope fay ]
   [gav  gay  eve  ivy  bea  cath abi  dee  hope jan  fay ]
   [hal  abi  eve  hope fay  ivy  cath jan  bea  gay  dee ]
   [ian  hope cath dee  gay  bea  abi  fay  ivy  jan  eve ]
   [jon  abi  fay  jan  gay  eve  bea  dee  cath ivy  hope]))

(define WOMEN

 '([abi  bob  fred jon  gav  ian  abe  dan  ed   col  hal ]
   [bea  bob  abe  col  fred gav  dan  ian  ed   jon  hal ]
   [cath fred bob  ed   gav  hal  col  ian  abe  dan  jon ]
   [dee  fred jon  col  abe  ian  hal  gav  dan  bob  ed  ]
   [eve  jon  hal  fred dan  abe  gav  col  ed   ian  bob ]
   [fay  bob  abe  ed   ian  jon  dan  fred gav  col  hal ]
   [gay  jon  gav  hal  fred bob  abe  col  ed   dan  ian ]
   [hope gav  jon  bob  abe  ian  dan  hal  ed   col  fred]
   [ivy  ian  col  hal  gav  fred bob  abe  ed   jon  dan ]
   [jan  ed   hal  gav  abe  bob  jon  col  ian  fred dan ]))
x is better than y according to the l order

(define (better? x y l) (memq y (cdr (memq x l))))

(define (stable-matching Mprefs Wprefs)

 (define M (map car Mprefs))
 (define engagements (make-hasheq))
 (define preferences (make-hasheq))
 (define (engage! m w)
   (hash-set! engagements m w)
   (hash-set! engagements w m))
 (for ([m Mprefs]) (hash-set! preferences (car m) (cdr m)))
 (for ([w Wprefs]) (hash-set! preferences (car w) (cdr w)))
 (let loop ()
   (define m+w
     (for/or ([m M])
       (and (not (hash-ref engagements m #f))   ; m is free
            (let ([p (hash-ref preferences m)]) ; can propose
              (and (pair? p)
                   (let ([w (car p)])
                     (hash-set! preferences m (cdr p)) ; drop w from m
                     (cons m w)))))))
   (when m+w
     (define m (car m+w))
     (define w (cdr m+w))
     (define m* (hash-ref engagements w #f))    ; m* is w's prev engagement
     (cond [(not m*) (engage! m w)]             ; w is free
           [(better? m m* (hash-ref preferences w)) ; w prefers m over m*
            (engage! m w)
            (hash-set! engagements m* #f)])     ; m* becomes free
     (loop)))
 engagements)

(define (find-unstable Mprefs Wprefs matches)

 (for*/or ([m (map car Mprefs)] [w (map car Wprefs)])
   (define w* (hash-ref matches m))
   (define m* (hash-ref matches w))
   (and (not (eq? m m*))
        (better? w w* (cdr (assq m Mprefs)))
        (better? m m* (cdr (assq w Wprefs)))
        (cons m w))))

(define (check-stability)

 (let ([u (find-unstable MEN WOMEN matches)])
   (if u
     (printf "Unstable: ~a and ~a prefer each other over partners.\n"
             (car u) (cdr u))
     (printf "The match is stable.\n"))))

(define matches (stable-matching MEN WOMEN)) (printf "Found matches:\n") (for ([m (map car MEN)]) (printf " ~a, ~a\n" m (hash-ref matches m))) (check-stability) (let ([M (map car (take (shuffle MEN) 2))])

 (printf "Swapping wives of ~a and ~a\n" (car M) (cadr M))
 (define (swap! x y)
   (define t (hash-ref matches x))
   (hash-set! matches x (hash-ref matches y))
   (hash-set! matches y t))
 (swap! (car M) (cadr M))
 (swap! (hash-ref matches (car M)) (hash-ref matches (cadr M))))

(check-stability) </lang>

Sample run:

Found matches:
  abe, ivy
  bob, cath
  col, dee
  dan, fay
  ed, jan
  fred, bea
  gav, gay
  hal, eve
  ian, hope
  jon, abi
The match is stable.
Swapping wives of bob and gav
Unstable: bob and abi prefer each other over partners.

REXX

Algorithm used: see link https://www.youtube.com/watch?v=Qcv1IqHWAzg <lang REXX>/*- REXX --------------------------------------------------------------

  • pref.b Preferences of boy b
  • pref.g Preferences of girl g
  • boys List of boys
  • girls List of girls
  • plist List of proposals
  • mlist List of (current) matches
  • glist List of girls to be matched
  • glist.b List of girls that proposed to boy b
  • blen maximum length of boys' names
  • glen maximum length of girls' names

*/

pref.Charlotte=translate('Bingley Darcy Collins Wickham ') pref.Elisabeth=translate('Wickham Darcy Bingley Collins ') pref.Jane =translate('Bingley Wickham Darcy Collins ') pref.Lydia =translate('Bingley Wickham Darcy Collins ')

pref.Bingley =translate('Jane Elisabeth Lydia Charlotte') pref.Collins =translate('Jane Elisabeth Lydia Charlotte') pref.Darcy =translate('Elisabeth Jane Charlotte Lydia') pref.Wickham =translate('Lydia Jane Elisabeth Charlotte')

pref.ABE='ABI EVE CATH IVY JAN DEE FAY BEA HOPE GAY' pref.BOB='CATH HOPE ABI DEE EVE FAY BEA JAN IVY GAY' pref.COL='HOPE EVE ABI DEE BEA FAY IVY GAY CATH JAN' pref.DAN='IVY FAY DEE GAY HOPE EVE JAN BEA CATH ABI' pref.ED='JAN DEE BEA CATH FAY EVE ABI IVY HOPE GAY' pref.FRED='BEA ABI DEE GAY EVE IVY CATH JAN HOPE FAY' pref.GAV='GAY EVE IVY BEA CATH ABI DEE HOPE JAN FAY' pref.HAL='ABI EVE HOPE FAY IVY CATH JAN BEA GAY DEE' pref.IAN='HOPE CATH DEE GAY BEA ABI FAY IVY JAN EVE' pref.JON='ABI FAY JAN GAY EVE BEA DEE CATH IVY HOPE'

pref.ABI='BOB FRED JON GAV IAN ABE DAN ED COL HAL' pref.BEA='BOB ABE COL FRED GAV DAN IAN ED JON HAL' pref.CATH='FRED BOB ED GAV HAL COL IAN ABE DAN JON' pref.DEE='FRED JON COL ABE IAN HAL GAV DAN BOB ED' pref.EVE='JON HAL FRED DAN ABE GAV COL ED IAN BOB' pref.FAY='BOB ABE ED IAN JON DAN FRED GAV COL HAL' pref.GAY='JON GAV HAL FRED BOB ABE COL ED DAN IAN' pref.HOPE='GAV JON BOB ABE IAN DAN HAL ED COL FRED' pref.IVY='IAN COL HAL GAV FRED BOB ABE ED JON DAN' pref.JAN='ED HAL GAV ABE BOB JON COL IAN FRED DAN'

If arg(1)> Then Do

 Say 'Input from task description'
 boys='ABE BOB COL DAN ED FRED GAV HAL IAN JON'
 girls='ABI BEA CATH DEE EVE FAY GAY HOPE IVY JAN'
 End

Else Do

 Say 'Input from link'
 girls=translate('Charlotte Elisabeth Jane  Lydia')
 boys =translate('Bingley   Collins   Darcy Wickham')
 End

debug=0 blen=0 Do i=1 To words(boys)

 blen=max(blen,length(word(boys,i)))
 End

glen=0 Do i=1 To words(girls)

 glen=max(glen,length(word(girls,i)))
 End

glist=girls mlist= Do ri=1 By 1 Until glist= /* as long as there are girls */

 Call dbg 'Round' ri
 plist=                             /* no proposals in this round */
 glist.=
 Do gi=1 To words(glist)              /* loop over free girls       */
   gg=word(glist,gi)                  /* an unmathed girl           */
   b=word(pref.gg,1)                  /* her preferred boy          */
   plist=plist gg'-'||b               /* remember this proposal     */
   glist.b=glist.b gg                 /* add girl to the boy's list */
   Call dbg left(gg,glen) 'proposes to' b  /* tell the user              */
   End
 Do bi=1 To words(boys)               /* loop over all boys         */
   b=word(boys,bi)                    /* one of them                */
   If glist.b> Then                 /* if he's got proposals      */
     Call dbg b 'has these proposals' glist.b /* show them               */
   End
 Do bi=1 To words(boys)               /* loop over all boys         */
   b=word(boys,bi)                    /* one of them                */
   bm=pos(b'*',mlist)                 /* has he been matched yet?   */
   Select
     When words(glist.b)=1 Then Do    /* one girl proposed for him  */
       gg=word(glist.b,1)             /* the proposing girl         */
       If bm=0 Then Do                /* no, he hasn't              */
         Call dbg b 'accepts' gg           /* is accepted                */
         Call set_mlist 'A',mlist b||'*'||gg /* add match to mlist  */
         Call set_glist 'A',remove(gg,glist) /* remove gg from glist*/
         pref.gg=remove(b,pref.gg)    /* remove b from gg's preflist*/
         End
       Else Do                        /* boy has been matched       */
         Parse Var mlist =(bm) '*' go ' ' /* to girl go             */
         If wordpos(gg,pref.b)<wordpos(go,pref.b) Then Do
              /* the proposing girl is preferred to the current one */
                                      /* so we replace go by gg     */
           Call set_mlist 'B',repl(mlist,b||'*'||gg,b||'*'||go)
           Call dbg b 'releases' go
           Call dbg b 'accepts ' gg
           Call set_glist 'B',glist go  /* add go to list of girls  */
           Call set_glist 'C',remove(gg,glist) /* and remove gg     */
           End
         pref.gg=remove(b,pref.gg)    /* remove b from gg's preflist*/
         End
       End
     When words(glist.b)>1 Then
       Call pick_1
     Otherwise Nop
     End
   End
 Call dbg 'Matches   :' mlist
 Call dbg 'free girls:' glist
 Call check 'L'
 End

Say 'Success at round' (ri-1) Do While mlist>

 Parse Var mlist boy '*' girl mlist
 Say left(boy,blen) 'matches' girl
 End

Exit

pick_1:

 If bm>0 Then Do                /* boy has been matched       */
   Parse Var mlist =(bm) '*' go ' ' /* to girl go             */
   pmin=wordpos(go,pref.b)
   End
 Else Do
   go=
   pmin=99
   End
 Do gi=1 To words(glist.b)
   gt=word(glist.b,gi)
   gp=wordpos(gt,pref.b)
   If gp<pmin Then Do
     pmin=gp
     gg=gt
     End
   End
 If bm=0 Then Do
   Call dbg b 'accepts' gg           /* is accepted                */
   Call set_mlist 'A',mlist b||'*'||gg /* add match to mlist  */
   Call set_glist 'A',remove(gg,glist) /* remove gg from glist*/
   pref.gg=remove(b,pref.gg)    /* remove b from gg's preflist*/
   End
 Else Do
   If gg<>go Then Do
     Call set_mlist 'B',repl(mlist,b||'*'||gg,b||'*'||go)
     Call dbg b 'releases' go
     Call dbg b 'accepts ' gg
     Call set_glist 'B',glist go  /* add go to list of girls  */
     Call set_glist 'C',remove(gg,glist) /* and remove gg     */
     pref.gg=remove(b,pref.gg)  /* remove b from gg's preflist*/
     End
   End
 Return

remove:

 Parse Arg needle,haystack
 pp=pos(needle,haystack)
 If pp>0 Then
   res=left(haystack,pp-1) substr(haystack,pp+length(needle))
 Else
   res=haystack
 Return space(res)

set_mlist:

 Parse Arg where,new_mlist
 Call dbg 'set_mlist' where':' mlist
 mlist=space(new_mlist)
 Call dbg 'set_mlist ->' mlist
 Call dbg 
 Return

set_glist:

 Parse Arg where,new_glist
 Call dbg 'set_glist' where':' glist
 glist=new_glist
 Call dbg 'set_glist ->' glist
 Call dbg 
 Return

check:

 If words(mlist)+words(glist)<>words(boys) Then Do
   Call dbg 'FEHLER bei' arg(1) (words(mlist)+words(glist))'<>10'
   say 'match='mlist'<'
   say '   glist='glist'<'
   End
 Return

dbg:

 If debug Then
   Call dbg arg(1)
 Return

repl: Procedure

 Parse Arg s,new,old
 Do i=1 To 100 Until p=0
   p=pos(old,s)
   If p>0 Then
     s=left(s,p-1)||new||substr(s,p+length(old))
   End
 Return s     </lang>
Output:
D:\>rexx smxa
Input from link
Success at round 5
BINGLEY matches LYDIA
WICKHAM matches JANE
DARCY   matches ELISABETH
COLLINS matches CHARLOTTE

D:\>rexx smxa .
Input from task description
Success at round 22
BOB  matches CATH
ED   matches JAN
FRED matches BEA
GAV  matches GAY
IAN  matches HOPE
JON  matches ABI
HAL  matches EVE
ABE  matches IVY
COL  matches DEE
DAN  matches FAY

Scala

Translation of: Java

<lang scala>import scala.collection.mutable.AbstractMap import scala.collection.mutable.HashMap import scala.collection.mutable.HashSet import scala.collection.mutable.Queue import scala.collection.mutable.TreeMap

object SMP extends App {

   def run() {
       val matches = matching(guys, guyPrefers, girlPrefers)
       matches.foreach { e => println(s"${e._1} is engaged to ${e._2}") }
       if (checkMatches(guys, girls, matches, guyPrefers, girlPrefers))
           println("Marriages are stable")
       else
           println("Marriages are unstable")
       val girl1 = girls.head
       val girl2 = girls(1)
       val tmp = matches(girl1)
       matches += girl1 -> matches(girl2)
       matches += girl2 -> tmp
       println(girl1 + " and " + girl2 + " have switched partners")
       if (checkMatches(guys, girls, matches, guyPrefers, girlPrefers))
           println("Marriages are stable")
       else
           println("Marriages are unstable")
   }
   private def matching(guys: Seq[String],
                        guyPrefers: AbstractMap[String, List[String]],
                        girlPrefers: AbstractMap[String, List[String]]): TreeMap[String, String] = {
       val engagements = new TreeMap[String, String]
       val freeGuys = new Queue[String]
       freeGuys ++= guys
       while (freeGuys.nonEmpty) {
           val guy = freeGuys.dequeue()
           val guy_p = guyPrefers(guy)
           var break = false
           for (girl <- guy_p)
               if (!break)
                   if (!engagements.contains(girl)) {
                       engagements += girl -> guy
                       break = true
                   }
                   else {
                       val other_guy = engagements(girl)
                       val girl_p = girlPrefers(girl)
                       if (girl_p.indexOf(guy) < girl_p.indexOf(other_guy)) {
                           engagements += girl -> guy
                           freeGuys += other_guy
                           break = true
                       }
                   }
       }
       engagements
   }
   private def checkMatches(guys: Seq[String], girls: Seq[String],
                            matches: AbstractMap[String, String],
                            guyPrefers: AbstractMap[String, List[String]],
                            girlPrefers: AbstractMap[String, List[String]]): Boolean = {
       if (!girls.toSet.subsetOf(matches.keySet) || !guys.toSet.subsetOf(HashSet() ++= matches.values))
           return false
       val invertedMatches = new TreeMap[String, String]
       matches.foreach { invertedMatches += _.swap }
       for ((k, v) <- matches) {
           val shePrefers = girlPrefers(k)
           val sheLikesBetter = Queue() ++= shePrefers.slice(0, shePrefers.indexOf(v))
           val hePrefers = guyPrefers(v)
           val heLikesBetter = Queue() ++= hePrefers.slice(0, hePrefers.indexOf(k))
           for (guy <- sheLikesBetter) {
               val fiance = invertedMatches(guy)
               val guy_p = guyPrefers(guy)
               if (guy_p.indexOf(fiance) > guy_p.indexOf(k)) {
                   println(s"$k likes $guy better than $v and $guy likes $k better than their current partner")
                   return false
               }
           }
           for (girl <- heLikesBetter) {
               val fiance = matches(girl)
               val girl_p = girlPrefers(girl)
               if (girl_p.indexOf(fiance) > girl_p.indexOf(v)) {
                   println(s"$v likes $girl better than $k and $girl likes $v better than their current partner")
                   return false
               }
           }
       }
       true
   }
   private val guys = "abe" :: "bob" :: "col" :: "dan" :: "ed" :: "fred" :: "gav" :: "hal" :: "ian" :: "jon" :: Nil
   private val girls = "abi" :: "bea" :: "cath" :: "dee" :: "eve" :: "fay" :: "gay" :: "hope" :: "ivy" :: "jan" :: Nil
   private val guyPrefers = HashMap("abe" -> List("abi", "eve", "cath", "ivy", "jan", "dee", "fay", "bea", "hope", "gay"),
       "bob" -> List("cath", "hope", "abi", "dee", "eve", "fay", "bea", "jan", "ivy", "gay"),
       "col" -> List("hope", "eve", "abi", "dee", "bea", "fay", "ivy", "gay", "cath", "jan"),
       "dan" -> List("ivy", "fay", "dee", "gay", "hope", "eve", "jan", "bea", "cath", "abi"),
       "ed" -> List("jan", "dee", "bea", "cath", "fay", "eve", "abi", "ivy", "hope", "gay"),
       "fred" -> List("bea", "abi", "dee", "gay", "eve", "ivy", "cath", "jan", "hope", "fay"),
       "gav" -> List("gay", "eve", "ivy", "bea", "cath", "abi", "dee", "hope", "jan", "fay"),
       "hal" -> List("abi", "eve", "hope", "fay", "ivy", "cath", "jan", "bea", "gay", "dee"),
       "ian" -> List("hope", "cath", "dee", "gay", "bea", "abi", "fay", "ivy", "jan", "eve"),
       "jon" -> List("abi", "fay", "jan", "gay", "eve", "bea", "dee", "cath", "ivy", "hope"))
   private val girlPrefers = HashMap("abi" -> List("bob", "fred", "jon", "gav", "ian", "abe", "dan", "ed", "col", "hal"),
       "bea" -> List("bob", "abe", "col", "fred", "gav", "dan", "ian", "ed", "jon", "hal"),
       "cath" -> List("fred", "bob", "ed", "gav", "hal", "col", "ian", "abe", "dan", "jon"),
       "dee" -> List("fred", "jon", "col", "abe", "ian", "hal", "gav", "dan", "bob", "ed"),
       "eve" -> List("jon", "hal", "fred", "dan", "abe", "gav", "col", "ed", "ian", "bob"),
       "fay" -> List("bob", "abe", "ed", "ian", "jon", "dan", "fred", "gav", "col", "hal"),
       "gay" -> List("jon", "gav", "hal", "fred", "bob", "abe", "col", "ed", "dan", "ian"),
       "hope" -> List("gav", "jon", "bob", "abe", "ian", "dan", "hal", "ed", "col", "fred"),
       "ivy" -> List("ian", "col", "hal", "gav", "fred", "bob", "abe", "ed", "jon", "dan"),
       "jan" -> List("ed", "hal", "gav", "abe", "bob", "jon", "col", "ian", "fred", "dan"))
   run()

}</lang>

Output:

See Java output.

Seed7

<lang seed7>$ include "seed7_05.s7i";

const type: preferences is hash [string] array string; const type: engaged is hash [string] string;

const func integer: pos (in array string: area, in string: searched) is func

 result
   var integer: pos is 1;
 begin
   while pos <= length(area) and area[pos] <> searched do
     incr(pos);
   end while;
   if pos > length(area) then
     pos := 0;
   end if;
 end func;

const func engaged: matchmaker (in preferences: guyPrefers, in preferences: girlPrefers) is func

 result
   var engaged: engagedTo is engaged.value;
 local
   var array string: freeGuys is 0 times "";
   var string: guy is "";
   var string: girl is "";
   var string: fiance is "";
   var array string: guyPreferencList is 0 times "";
   var array string: girlPreferenceList is 0 times "";
   var boolean: searching is TRUE;
 begin
   freeGuys := sort(keys(guyPrefers));
   while length(freeGuys) <> 0 do
     guy := freeGuys[1];
     freeGuys := freeGuys[2 ..];
     guyPreferencList := guyPrefers[guy];
     searching := TRUE;
     while searching and length(guyPreferencList) <> 0 do
       girl := guyPreferencList[1];
       guyPreferencList := guyPreferencList[2 ..];
       if girl not in engagedTo then
         engagedTo @:= [girl] guy;
         writeln("  " <& girl <& " and " <& guy);
         searching := FALSE;
       else
         fiance := engagedTo[girl];
         girlPreferenceList := girlPrefers[girl];
         if pos(girlPreferenceList, guy) < pos(girlPreferenceList, fiance) then
           # She prefers new guy
           engagedTo @:= [girl] guy;
           freeGuys &:= fiance;
           writeln("  " <& girl <& " dumped " <& fiance <& " for " <& guy);
           searching := FALSE;
         end if;
       end if;
     end while;
   end while;
 end func;

const func boolean: check (in engaged: engagedTo,

   in preferences: guyPrefers, in preferences: girlPrefers) is func
 result
   var boolean: stable is TRUE;
 local
   var string: he is "";
   var string: she is "";
   var string: guy is "";
   var string: girl is "";
   var engaged: inverseEngaged is engaged.value;
   var array string: sheLikes is 0 times "";
   var array string: sheLikesBetter is 0 times "";
   var array string: heLikes is 0 times "";
   var array string: heLikesBetter is 0 times "";
   var string: guysGirl is "";
   var array string: guyLikes is 0 times "";
   var string: girlsGuy is "";
   var array string: girlLikes is 0 times "";
 begin
   for he key she range engagedTo do
     inverseEngaged @:= [he] she;
   end for;
   for he key she range engagedTo do
     sheLikes := girlPrefers[she];
     sheLikesBetter := sheLikes[.. pred(pos(sheLikes, he))];
     heLikes := guyPrefers[he];
     heLikesBetter := heLikes[.. pred(pos(heLikes, she))];
     for guy range sheLikesBetter do
       guysGirl := inverseEngaged[guy];
       guyLikes := guyPrefers[guy];
       if pos(guyLikes, guysGirl) > pos(guyLikes, she) and stable then
         writeln(she <& " likes " <& guy <& " better than " <& he <& " and " <&
                 guy <& " likes " <& she <& " better than their current partner");
         stable := FALSE;
       end if;
     end for;
     for girl range heLikesBetter do
       girlsGuy := engagedTo[girl];
       girlLikes := girlPrefers[girl];
       if pos(girlLikes, girlsGuy) > pos(girlLikes, he) and stable then
         writeln(he <& " likes " <& girl <& " better than " <& she <& " and " <&
                 girl <& " likes " <& he <& " better than their current partner");
         stable := FALSE;
       end if;
     end for;
   end for;
 end func;

var preferences: guyPrefers is preferences.value; var preferences: girlPrefers is preferences.value; guyPrefers @:= ["abe"] [] ("abi", "eve", "cath", "ivy", "jan", "dee", "fay", "bea", "hope", "gay"); guyPrefers @:= ["bob"] [] ("cath", "hope", "abi", "dee", "eve", "fay", "bea", "jan", "ivy", "gay"); guyPrefers @:= ["col"] [] ("hope", "eve", "abi", "dee", "bea", "fay", "ivy", "gay", "cath", "jan"); guyPrefers @:= ["dan"] [] ("ivy", "fay", "dee", "gay", "hope", "eve", "jan", "bea", "cath", "abi"); guyPrefers @:= ["ed"] [] ("jan", "dee", "bea", "cath", "fay", "eve", "abi", "ivy", "hope", "gay"); guyPrefers @:= ["fred"] [] ("bea", "abi", "dee", "gay", "eve", "ivy", "cath", "jan", "hope", "fay"); guyPrefers @:= ["gav"] [] ("gay", "eve", "ivy", "bea", "cath", "abi", "dee", "hope", "jan", "fay"); guyPrefers @:= ["hal"] [] ("abi", "eve", "hope", "fay", "ivy", "cath", "jan", "bea", "gay", "dee"); guyPrefers @:= ["ian"] [] ("hope", "cath", "dee", "gay", "bea", "abi", "fay", "ivy", "jan", "eve"); guyPrefers @:= ["jon"] [] ("abi", "fay", "jan", "gay", "eve", "bea", "dee", "cath", "ivy", "hope"); girlPrefers @:= ["abi"] [] ("bob", "fred", "jon", "gav", "ian", "abe", "dan", "ed", "col", "hal"); girlPrefers @:= ["bea"] [] ("bob", "abe", "col", "fred", "gav", "dan", "ian", "ed", "jon", "hal"); girlPrefers @:= ["cath"] [] ("fred", "bob", "ed", "gav", "hal", "col", "ian", "abe", "dan", "jon"); girlPrefers @:= ["dee"] [] ("fred", "jon", "col", "abe", "ian", "hal", "gav", "dan", "bob", "ed"); girlPrefers @:= ["eve"] [] ("jon", "hal", "fred", "dan", "abe", "gav", "col", "ed", "ian", "bob"); girlPrefers @:= ["fay"] [] ("bob", "abe", "ed", "ian", "jon", "dan", "fred", "gav", "col", "hal"); girlPrefers @:= ["gay"] [] ("jon", "gav", "hal", "fred", "bob", "abe", "col", "ed", "dan", "ian"); girlPrefers @:= ["hope"] [] ("gav", "jon", "bob", "abe", "ian", "dan", "hal", "ed", "col", "fred"); girlPrefers @:= ["ivy"] [] ("ian", "col", "hal", "gav", "fred", "bob", "abe", "ed", "jon", "dan"); girlPrefers @:= ["jan"] [] ("ed", "hal", "gav", "abe", "bob", "jon", "col", "ian", "fred", "dan");

const proc: main is func

 local
   var engaged: engagedTo is engaged.value;
   var string: girl is "";
 begin
   writeln("Matchmaking:");
   engagedTo := matchmaker(guyPrefers, girlPrefers);
   writeln;
   writeln("Engagements:");
   for girl range sort(keys(engagedTo)) do
     writeln("  " <& girl <& " and " <& engagedTo[girl]);
   end for;
   writeln;
   writeln("Marriages are " <& [] ("unstable", "stable") [succ(ord(check(engagedTo, guyPrefers, girlPrefers)))]);
   writeln;
   writeln("Perturb:");
   engagedTo @:= ["abi"] "fred";
   engagedTo @:= ["bea"] "jon";
   writeln("engage abi with fred and bea with jon");
   writeln;
   writeln("Marriages are " <& [] ("unstable", "stable") [succ(ord(check(engagedTo, guyPrefers, girlPrefers)))]);
 end func;</lang>

Output:

Matchmaking:
  abi and abe
  cath and bob
  hope and col
  ivy and dan
  jan and ed
  bea and fred
  gay and gav
  eve and hal
  hope dumped col for ian
  abi dumped abe for jon
  dee and col
  ivy dumped dan for abe
  fay and dan

Engagements:
  abi and jon
  bea and fred
  cath and bob
  dee and col
  eve and hal
  fay and dan
  gay and gav
  hope and ian
  ivy and abe
  jan and ed

Marriages are stable

Perturb:
engage abi with fred and bea with jon

bea likes fred better than jon and fred likes bea better than their current partner
Marriages are unstable

Sidef

Translation of: Perl 6

<lang ruby>var he_likes = Hash(

   abe  => < abi eve cath ivy jan dee fay bea hope gay >,
   bob  => < cath hope abi dee eve fay bea jan ivy gay >,
   col  => < hope eve abi dee bea fay ivy gay cath jan >,
   dan  => < ivy fay dee gay hope eve jan bea cath abi >,
   ed   => < jan dee bea cath fay eve abi ivy hope gay >,
   fred => < bea abi dee gay eve ivy cath jan hope fay >,
   gav  => < gay eve ivy bea cath abi dee hope jan fay >,
   hal  => < abi eve hope fay ivy cath jan bea gay dee >,
   ian  => < hope cath dee gay bea abi fay ivy jan eve >,
   jon  => < abi fay jan gay eve bea dee cath ivy hope >,

);

var she_likes = Hash(

   abi  => < bob fred jon gav ian abe dan ed col hal >,
   bea  => < bob abe col fred gav dan ian ed jon hal >,
   cath => < fred bob ed gav hal col ian abe dan jon >,
   dee  => < fred jon col abe ian hal gav dan bob ed >,
   eve  => < jon hal fred dan abe gav col ed ian bob >,
   fay  => < bob abe ed ian jon dan fred gav col hal >,
   gay  => < jon gav hal fred bob abe col ed dan ian >,
   hope => < gav jon bob abe ian dan hal ed col fred >,
   ivy  => < ian col hal gav fred bob abe ed jon dan >,
   jan  => < ed hal gav abe bob jon col ian fred dan >,

);

var guys = he_likes.keys; var gals = she_likes.keys;

var (:fiancé, :fiancée, :proposed);

func she_prefers (her, hottie) { var a = she_likes{her}; a.index(hottie) < a.index(fiancé{her}) } func he_prefers (him, hottie) { var a = he_likes{him}; a.index(hottie) < a.index(fiancée{him}) }

func unmatched_guy { guys.first {|k| !defined fiancée{k} } } func preferred_choice(guy) { he_likes{guy}.first {|k| !defined proposed{guy}{k} } }

func engage(guy, gal) {

   fiancé{gal} = guy;
   fiancée{guy} = gal;

}

func match_em {

   say 'Matchmaking:';
   while (defined(var guy = unmatched_guy())) {
       var gal = preferred_choice(guy);
       proposed{guy}{gal} = '❤';
       if (!defined fiancé{gal}) {
           engage(guy, gal);
           say "\t#{gal} and #{guy}";
       }
       elsif (she_prefers(gal, guy)) {
           var engaged_guy = fiancé{gal};
           engage(guy, gal);
           fiancée{engaged_guy} = nil;
           say "\t#{gal} dumped #{engaged_guy} for #{guy}";
       }
   }

}

func check_stability {

   var instabilities = gather {
       guys.each { |m|
           gals.each { |w|
               if (he_prefers(m, w) && she_prefers(w, m)) {
                   take "\t#{w} prefers #{m} to #{fiancé{w}} and #{m} prefers #{w} to #{fiancée{m}}";
               }
           }
       }
   }
   say 'Stablility:';
   instabilities.is_empty
       ? say "\t(all marriages stable)"
       : instabilities.each { |i| say i };

}

func perturb_em {

   say 'Perturb:';
   say "\tengage abi with fred and bea with jon";
   engage('fred', 'abi');
   engage('jon', 'bea');

}

match_em(); check_stability();

perturb_em(); check_stability();</lang>

Output:
Matchmaking:
	abi and jon
	eve and abe
	bea and fred
	cath and bob
	hope and ian
	eve dumped abe for hal
	ivy and abe
	dee and col
	jan and ed
	fay and dan
	gay and gav
Stablility:
	(all marriages stable)
Perturb:
	engage abi with fred and bea with jon
Stablility:
	gay prefers jon to gav and jon prefers gay to bea
	eve prefers jon to hal and jon prefers eve to bea
	fay prefers jon to dan and jon prefers fay to bea
	bea prefers fred to jon and fred prefers bea to abi

SPARK / Ada

Works with: SPARK GPL
Works with: GNAT

This solution works for Ada, too, since SPARK code is correct Ada code.

The data set package: <lang ada>package Preferences is

  type Guy_X is (no_guy, abe, bob, col, dan, ed, fred, gav, hal, ian, jon);
  subtype Guy is Guy_X range Guy_X'Succ(Guy_X'First) .. Guy_X'Last;
  type Girl_X is (no_girl, abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan);
  subtype Girl is Girl_X range Girl_X'Succ(Girl_X'First) .. Girl_X'Last;
  type Extended_Rank is range 0 .. 10;
  subtype Rank is Extended_Rank range 1 .. Extended_Rank'Last;
  type His_Rank is array (Rank) of Girl;
  type He_Prefers is array (Guy) of His_Rank;
  Guys_Like : constant He_Prefers := He_Prefers'(
    abe  => His_Rank'(abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay),
    bob  => His_Rank'(cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay),
    col  => His_Rank'(hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan),
    dan  => His_Rank'(ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi),
    ed   => His_Rank'(jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay),
    fred => His_Rank'(bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay),
    gav  => His_Rank'(gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay),
    hal  => His_Rank'(abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee),
    ian  => His_Rank'(hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve),
    jon  => His_Rank'(abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope));
  type Her_Rank is array(Rank) of Guy;
  type She_Prefers is array (Girl) of Her_Rank;
  Girls_Like : constant She_Prefers := She_Prefers'(
    abi  => Her_Rank'(bob, fred, jon, gav, ian, abe, dan, ed, col, hal),
    bea  => Her_Rank'(bob, abe, col, fred, gav, dan, ian, ed, jon, hal),
    cath => Her_Rank'(fred, bob, ed, gav, hal, col, ian, abe, dan, jon),
    dee  => Her_Rank'(fred, jon, col, abe, ian, hal, gav, dan, bob, ed),
    eve  => Her_Rank'(jon, hal, fred, dan, abe, gav, col, ed, ian, bob),
    fay  => Her_Rank'(bob, abe, ed, ian, jon, dan, fred, gav, col, hal),
    gay  => Her_Rank'(jon, gav, hal, fred, bob, abe, col, ed, dan, ian),
    hope => Her_Rank'(gav, jon, bob, abe, ian, dan, hal, ed, col, fred),
    ivy  => Her_Rank'(ian, col, hal, gav, fred, bob, abe, ed, jon, dan),
    jan  => Her_Rank'(ed, hal, gav, abe, bob, jon, col, ian, fred, dan));

end Preferences; </lang> The package for creating the engagements and checking stability. This package can be analysed by the SPARK tools and proved to be free of any run-time error. <lang ada>with Preferences; --# inherit Preferences; package Propose is

  type Engagements is array (Preferences.Girl) of Preferences.Guy_X;
  procedure Engage (Pairs :    out Engagements);
  --# derives Pairs from ;
  procedure Check_Stable (Pairs      : in     Engagements;
                          OK         :    out Boolean;
                          Other_Girl :    out Preferences.Girl_X;
                          Other_Guy  :    out Preferences.Guy_X);
  --# derives OK,
  --#         Other_Girl,
  --#         Other_Guy from Pairs;

end Propose; </lang> <lang ada>with Preferences; use type Preferences.Extended_Rank; use type Preferences.Girl; use type Preferences.Guy; package body Propose is

  --  renaming subtypes:
  subtype Guy  is Preferences.Guy;
  subtype Girl is Preferences.Girl;
  function Her_Rank_Of_Him (Her : Girl;
                            Him : Guy) return Preferences.Rank
  is
     R : Preferences.Rank;
  begin
     R := Preferences.Rank'First;
     while Preferences.Girls_Like(Her)(R) /= Him
       and R /= Preferences.Rank'Last
     loop
        R := Preferences.Rank'Succ(R);
     end loop;
     return R;
  end Her_Rank_Of_Him;
  function His_Rank_Of_Her (Him : Guy;
                            Her : Girl) return Preferences.Rank
  is
     R : Preferences.Rank;
  begin
     R := Preferences.Rank'First;
     while Preferences.Guys_Like(Him)(R) /= Her
       and R /= Preferences.Rank'Last
     loop
        R := Preferences.Rank'Succ(R);
     end loop;
     return R;
  end His_Rank_Of_Her;
  procedure Engage (Pairs :    out Engagements)
  is
     type Free_Guy  is array (Guy)  of Boolean;
     type Free_Girl is array (Girl) of Boolean;
     type Last_Proposals is array (Guy) of Preferences.Extended_Rank;
     --  Initialize all M in M_Free and W in W_Free to free.
     M_Free : Free_Guy  := Free_Guy'(others => True);
     W_Free : Free_Girl := Free_Girl'(others => True);
     Last_Proposal : Last_Proposals :=
       Last_Proposals'(others => Preferences.Extended_Rank'First);
     All_Paired : Boolean := False;
     W  : Girl;
     M1 : Preferences.Guy_X;
  begin
     --  Initially set all engagements to null.
     Pairs := Engagements'(others => Preferences.No_Guy);
     --  while there is a free man M who still has a woman W to propose to
     while not All_Paired loop
        All_Paired := True;
        for M in Guy loop
           if M_Free(M) and Last_Proposal(M) < Preferences.Rank'Last then
              All_Paired := False;
              --  W = M's highest ranked such woman who he has not
              --            proposed to yet
              Last_Proposal(M) := Preferences.Rank'Succ(Last_Proposal(M));
              W := Preferences.Guys_Like(M)(Last_Proposal(M));
              --  if W is free
              if W_Free(W) then
                 --  (M, W) become engaged
                 M_Free(M) := False;
                 W_Free(W) := False;
                 Pairs(W)  := M;
              else
                 --  else some pair (M1, W) already exists
                 M1 := Pairs(W);
                 if M1 > Preferences.no_guy and then
                 --  if W prefers M to M1
                   Her_Rank_Of_Him (Her => W, Him => M)
                   < Her_Rank_Of_Him (Her => W, Him => M1)
                 then
                    --  (M, W) become engaged
                    M_Free(M) := False;
                    Pairs(W)  := M;
                    --  M1 becomes free
                    M_Free(M1) := True;
                 else
                    --  (M1, W) remain engaged
                    null;
                 end if;
              end if;
           end if;
        end loop;
     end loop;
  end Engage;
  procedure Check_Stable (Pairs      : in     Engagements;
                          OK         :    out Boolean;
                          Other_Girl :    out Preferences.Girl_X;
                          Other_Guy  :    out Preferences.Guy_X)
  is
     M      : Preferences.Guy_X;
     W_Rank : Preferences.Rank;
  begin
     OK := True;
     Other_Girl := Preferences.No_Girl;
     Other_Guy  := Preferences.No_Guy;
     --  Loop over all girls.
     for W in Girl loop
        if Pairs(W) > Preferences.no_guy then
           W_Rank := Her_Rank_Of_Him (W, Pairs(W));
           --  Loop over all guys she prefers to her current guy.
           for WR in Preferences.Rank range 1 .. W_Rank - 1 loop
              M := Preferences.Girls_Like(W)(WR);
              if M > Preferences.no_guy then
                 --  Loop over all girls for this guy in preference order.
                 for MR in Preferences.Rank
                 --# assert M > Preferences.no_guy;
                 loop
                    --  Exit if his current girl found before this girl.
                    exit when M = Pairs(Preferences.Guys_Like(M)(MR));
                    --  Unstable if this girl found before his current girl.
                    if Preferences.Guys_Like(M)(MR) = W then
                       OK := False;
                       Other_Girl := W;
                       Other_Guy  := M;
                    end if;
                 end loop;
              end if;
              exit when not OK;
           end loop;
        end if;
        exit when not OK;
     end loop;
  end Check_Stable;

end Propose; </lang> The test program tests all pairwise exchanges. This is Ada, it is not SPARK.

(Text IO is quite tedious in SPARK - it's not what the language was designed for.) <lang ada>------------------------------------ -- Test program. -- -- This is Ada, it is not SPARK.


with Ada.Text_IO; with Preferences; with Propose; procedure Matchmaker is

  --  renaming subtypes:
  subtype Guy  is Preferences.Guy;
  subtype Girl is Preferences.Girl;
  Marriages : Propose.Engagements;
  Stable    : Boolean;
  Him       : Preferences.Guy_X;
  Her       : Preferences.Girl_X;
  Stable_Marriages : Propose.Engagements;
  procedure Report_Stable
  is
  begin
     if Stable then
        Ada.Text_IO.Put_Line ("Pairs are Stable");
     else
        Ada.Text_IO.Put ("Pairs are Unstable: ");
        Ada.Text_IO.Put_Line
          (Guy'Image(Him) & " and " & Girl'Image(Her) & " prefer each other.");
     end if;
  end Report_Stable;

begin

  Propose.Engage(Pairs => Marriages);
  for W in Girl loop
     Ada.Text_IO.Put_Line (Girl'Image(W) &
                           " marries " &
                           Guy'Image(Marriages(W)));
  end loop;
  Propose.Check_Stable (Pairs      => Marriages,
                        OK         => Stable,
                        Other_Girl => Her,
                        Other_Guy  => Him);
  Report_Stable;
  Stable_Marriages := Marriages;
  for W1 in Girl range Girl'First .. Girl'Pred(Girl'Last) loop
     for W2 in Girl range Girl'Succ(W1) .. Girl'Last loop
        Ada.Text_IO.New_Line;
        Ada.Text_IO.Put_Line ("Exchange " & Guy'Image(Marriages(W1)) &
                              " with " & Guy'Image(Marriages(W2)));
        Him := Marriages(W1);
        Marriages(W1) := Marriages(W2);
        Marriages(W2) := Him;
        Propose.Check_Stable (Pairs      => Marriages,
                              OK         => Stable,
                              Other_Girl => Her,
                              Other_Guy  => Him);
        Report_Stable;
        Marriages := Stable_Marriages;
     end loop;
  end loop;

end MatchMaker; </lang> The begining of the output from the test. All pairwise exchanges create unstable pairings.

ABI marries JON
BEA marries FRED
CATH marries BOB
DEE marries COL
EVE marries HAL
FAY marries DAN
GAY marries GAV
HOPE marries IAN
IVY marries ABE
JAN marries ED
Pairs are Stable

Exchange JON with FRED
Pairs are Unstable: FRED and BEA prefer each other.

Exchange JON with BOB
Pairs are Unstable: BOB and CATH prefer each other.

Exchange JON with COL
Pairs are Unstable: JON and ABI prefer each other.

Swift

Translation of: JavaScript

<lang Swift>class Person {

   let name:String
   var candidateIndex = 0
   var fiance:Person?
   var candidates = [Person]()
   
   init(name:String) {
       self.name = name
   }
   
   func rank(p:Person) -> Int {
       for (i, candidate) in enumerate(self.candidates) {
           if candidate === p {
               return i
           }
       }
       return self.candidates.count + 1
   }
   
   func prefers(p:Person) -> Bool {
       if let fiance = self.fiance {
           return self.rank(p) < self.rank(fiance)
       }
       return false
   }
   
   func nextCandidate() -> Person? {
       if self.candidateIndex >= self.candidates.count {
           return nil
       }
       return self.candidates[candidateIndex++]
   }
   
   func engageTo(p:Person) {
       p.fiance?.fiance = nil
       p.fiance = self
       self.fiance?.fiance = nil
       self.fiance = p
   }
   
   func swapWith(p:Person) {
       let thisFiance = self.fiance
       let pFiance = p.fiance
       println("\(self.name) swapped partners with \(p.name)")
       if pFiance != nil && thisFiance != nil {
           self.engageTo(pFiance!)
           p.engageTo(thisFiance!)
       }
   }

}

func isStable(guys:[Person], gals:[Person]) -> Bool {

   for guy in guys {
       for gal in gals {
           if guy.prefers(gal) && gal.prefers(guy) {
               return false
           }
       }
   }
   return true

}

func engageEveryone(guys:[Person]) {

   var done = false
   while !done {
       done = true
       for guy in guys {
           if guy.fiance == nil {
               done = false
               if let gal = guy.nextCandidate() {
                   if gal.fiance == nil || gal.prefers(guy) {
                       guy.engageTo(gal)
                   }
               }
           }
       }
   }

}

func doMarriage() {

   let abe  = Person(name: "Abe")
   let bob  = Person(name: "Bob")
   let col  = Person(name: "Col")
   let dan  = Person(name: "Dan")
   let ed   = Person(name: "Ed")
   let fred = Person(name: "Fred")
   let gav  = Person(name: "Gav")
   let hal  = Person(name: "Hal")
   let ian  = Person(name: "Ian")
   let jon  = Person(name: "Jon")
   let abi  = Person(name: "Abi")
   let bea  = Person(name: "Bea")
   let cath = Person(name: "Cath")
   let dee  = Person(name: "Dee")
   let eve  = Person(name: "Eve")
   let fay  = Person(name: "Fay")
   let gay  = Person(name: "Gay")
   let hope = Person(name: "Hope")
   let ivy  = Person(name: "Ivy")
   let jan  = Person(name: "Jan")
   
   abe.candidates  = [abi, eve, cath, ivy, jan, dee, fay, bea, hope, gay]
   bob.candidates  = [cath, hope, abi, dee, eve, fay, bea, jan, ivy, gay]
   col.candidates  = [hope, eve, abi, dee, bea, fay, ivy, gay, cath, jan]
   dan.candidates  = [ivy, fay, dee, gay, hope, eve, jan, bea, cath, abi]
   ed.candidates   = [jan, dee, bea, cath, fay, eve, abi, ivy, hope, gay]
   fred.candidates = [bea, abi, dee, gay, eve, ivy, cath, jan, hope, fay]
   gav.candidates  = [gay, eve, ivy, bea, cath, abi, dee, hope, jan, fay]
   hal.candidates  = [abi, eve, hope, fay, ivy, cath, jan, bea, gay, dee]
   ian.candidates  = [hope, cath, dee, gay, bea, abi, fay, ivy, jan, eve]
   jon.candidates  = [abi, fay, jan, gay, eve, bea, dee, cath, ivy, hope]
   abi.candidates  = [bob, fred, jon, gav, ian, abe, dan, ed, col, hal]
   bea.candidates  = [bob, abe, col, fred, gav, dan, ian, ed, jon, hal]
   cath.candidates = [fred, bob, ed, gav, hal, col, ian, abe, dan, jon]
   dee.candidates  = [fred, jon, col, abe, ian, hal, gav, dan, bob, ed]
   eve.candidates  = [jon, hal, fred, dan, abe, gav, col, ed, ian, bob]
   fay.candidates  = [bob, abe, ed, ian, jon, dan, fred, gav, col, hal]
   gay.candidates  = [jon, gav, hal, fred, bob, abe, col, ed, dan, ian]
   hope.candidates = [gav, jon, bob, abe, ian, dan, hal, ed, col, fred]
   ivy.candidates  = [ian, col, hal, gav, fred, bob, abe, ed, jon, dan]
   jan.candidates  = [ed, hal, gav, abe, bob, jon, col, ian, fred, dan]
   
   let guys = [abe, bob, col, dan, ed, fred, gav, hal, ian, jon]
   let gals = [abi, bea, cath, dee, eve, fay, gay, hope, ivy, jan]
   
   engageEveryone(guys)
   
   for guy in guys {
       println("\(guy.name) is engaged to \(guy.fiance!.name)")
   }
   
   println("Stable = \(isStable(guys, gals))")
   jon.swapWith(fred)
   println("Stable = \(isStable(guys, gals))")
   

}

doMarriage()</lang>

Output:
Abe is engaged to Ivy
Bob is engaged to Cath
Col is engaged to Dee
Dan is engaged to Fay
Ed is engaged to Jan
Fred is engaged to Bea
Gav is engaged to Gay
Hal is engaged to Eve
Ian is engaged to Hope
Jon is engaged to Abi
Stable = true
Jon swapped partners with Fred
Stable = false

Tcl

Translation of: Python

<lang tcl>package require Tcl 8.5

  1. Functions as aliases to standard commands

interp alias {} tcl::mathfunc::pos {} ::lsearch -exact interp alias {} tcl::mathfunc::nonempty {} ::llength

  1. The stability check

proc check engaged {

   global preferences
   set inverse [lreverse $engaged]
   set errmsg "%s and %s like each other better than their present partners,\

%s and %s respectively"

   dict for {she he} $engaged {

set shelikes [dict get $preferences $she] set shelikesbetter [lrange $shelikes 0 [expr {pos($shelikes,$he)}]] set helikes [dict get $preferences $he] set helikesbetter [lrange $helikes 0 [expr {pos($helikes,$she)}]] foreach guy $shelikesbetter { set guysgirl [dict get $inverse $guy] set guylikes [dict get $preferences $guy] if {pos($guylikes,$guysgirl) > pos($guylikes,$she)} { puts [format $errmsg $she $guy $he $guysgirl] return 0 } } foreach gal $helikesbetter { set galsguy [dict get $engaged $gal] set gallikes [dict get $preferences $gal] if {pos($gallikes,$galsguy) > pos($gallikes,$he)} { puts [format $errmsg $he $gal $she $galsguy] return 0 } }

   }
   return 1

}

  1. The match-making algorithm

proc matchmaker {} {

   global guys gals preferences
   set guysfree $guys
   set engaged {}
   array set p $preferences
   while {nonempty($guysfree)} {

set guysfree [lassign $guysfree guy] set p($guy) [set guyslist [lassign $p($guy) gal]] if {![dict exists $engaged $gal]} { # She's free dict set engaged $gal $guy puts " $guy and $gal" continue } # The bounder proposes to an engaged lass! set fiance [dict get $engaged $gal] if {pos($p($gal), $fiance) > pos($p($gal), $guy)} { # She prefers the new guy dict set engaged $gal $guy puts " $gal dumped $fiance for $guy" set guy $fiance } if {nonempty($p($guy))} { lappend guysfree $guy }

   }
   return $engaged

}

  1. Problem dataset; preferences unified since all names distinct

set guys {abe bob col dan ed fred gav hal ian jon} set gals {abi bea cath dee eve fay gay hope ivy jan} set preferences {

   abe  {abi  eve  cath ivy  jan  dee  fay  bea  hope gay}
   bob  {cath hope abi  dee  eve  fay  bea  jan  ivy  gay}
   col  {hope eve  abi  dee  bea  fay  ivy  gay  cath jan}
   dan  {ivy  fay  dee  gay  hope eve  jan  bea  cath abi}
   ed   {jan  dee  bea  cath fay  eve  abi  ivy  hope gay}
   fred {bea  abi  dee  gay  eve  ivy  cath jan  hope fay}
   gav  {gay  eve  ivy  bea  cath abi  dee  hope jan  fay}
   hal  {abi  eve  hope fay  ivy  cath jan  bea  gay  dee}
   ian  {hope cath dee  gay  bea  abi  fay  ivy  jan  eve}
   jon  {abi  fay  jan  gay  eve  bea  dee  cath ivy  hope}
   abi  {bob  fred jon  gav  ian  abe dan  ed  col  hal}
   bea  {bob  abe  col  fred gav  dan ian  ed  jon  hal}
   cath {fred bob  ed   gav  hal  col ian  abe dan  jon}
   dee  {fred jon  col  abe  ian  hal gav  dan bob  ed}
   eve  {jon  hal  fred dan  abe  gav col  ed  ian  bob}
   fay  {bob  abe  ed   ian  jon  dan fred gav col  hal}
   gay  {jon  gav  hal  fred bob  abe col  ed  dan  ian}
   hope {gav  jon  bob  abe  ian  dan hal  ed  col  fred}
   ivy  {ian  col  hal  gav  fred bob abe  ed  jon  dan}
   jan  {ed   hal  gav  abe  bob  jon col  ian fred dan}

}

  1. The demonstration code

puts "Engagements:" set engaged [matchmaker]

puts "\nCouples:" set pfx "" foreach gal $gals {

   puts -nonewline "$pfx  $gal is engaged to [dict get $engaged $gal]"
   set pfx ",\n"

} puts "\n" puts "Engagement stability check [lindex {FAILED PASSED} [check $engaged]]"

puts "\n\nSwapping two fiances to introduce an error" set tmp [dict get $engaged [lindex $gals 0]] dict set engaged [lindex $gals 0] [dict get $engaged [lindex $gals 1]] dict set engaged [lindex $gals 1] $tmp foreach gal [lrange $gals 0 1] {

   puts "  $gal is now engaged to [dict get $engaged $gal]"

} puts "" puts "Engagement stability check [lindex {FAILED PASSED} [check $engaged]]"</lang>

Output:
Engagements:
  abe and abi
  bob and cath
  col and hope
  dan and ivy
  ed and jan
  fred and bea
  gav and gay
  hope dumped col for ian
  abi dumped abe for jon
  hal and eve
  col and dee
  ivy dumped dan for abe
  dan and fay

Couples:
  abi is engaged to jon,
  bea is engaged to fred,
  cath is engaged to bob,
  dee is engaged to col,
  eve is engaged to hal,
  fay is engaged to dan,
  gay is engaged to gav,
  hope is engaged to ian,
  ivy is engaged to abe,
  jan is engaged to ed

Engagement stability check PASSED


Swapping two fiances to introduce an error
  abi is now engaged to fred
  bea is now engaged to jon

fred and bea like each other better than their present partners, abi and jon respectively
Engagement stability check FAILED

UNIX Shell

Works with: Bourne Again Shell version 4.0
Translation of: AutoHotkey

<lang shell>#!/usr/bin/env bash main() {

 # Our ten males:
 local males=(abe bob col dan ed fred gav hal ian jon)
 # And ten females:
 local females=(abi bea cath dee eve fay gay hope ivy jan)
 # Everyone's preferences, ranked most to least desirable:
 local  abe=( abi  eve  cath ivy  jan  dee  fay  bea  hope gay )
 local  abi=( bob  fred jon  gav  ian  abe  dan  ed   col  hal )
 local  bea=( bob  abe  col  fred gav  dan  ian  ed   jon  hal )
 local  bob=(cath  hope abi  dee  eve  fay  bea  jan  ivy  gay )
 local cath=(fred  bob  ed   gav  hal  col  ian  abe  dan  jon )
 local  col=(hope  eve  abi  dee  bea  fay  ivy  gay  cath jan )
 local  dan=( ivy  fay  dee  gay  hope eve  jan  bea  cath abi )
 local  dee=(fred  jon  col  abe  ian  hal  gav  dan  bob  ed  )
 local   ed=( jan  dee  bea  cath fay  eve  abi  ivy  hope gay )
 local  eve=( jon  hal  fred dan  abe  gav  col  ed   ian  bob )
 local  fay=( bob  abe  ed   ian  jon  dan  fred gav  col  hal )
 local fred=( bea  abi  dee  gay  eve  ivy  cath jan  hope fay )
 local  gav=( gay  eve  ivy  bea  cath abi  dee  hope jan  fay )
 local  gay=( jon  gav  hal  fred bob  abe  col  ed   dan  ian )
 local  hal=( abi  eve  hope fay  ivy  cath jan  bea  gay  dee )
 local hope=( gav  jon  bob  abe  ian  dan  hal  ed   col  fred)
 local  ian=(hope  cath dee  gay  bea  abi  fay  ivy  jan  eve )
 local  ivy=( ian  col  hal  gav  fred bob  abe  ed   jon  dan )
 local  jan=( ed   hal  gav  abe  bob  jon  col  ian  fred dan )
 local  jon=( abi  fay  jan  gay  eve  bea  dee  cath ivy  hope)
 # A place to store the engagements:
 local -A engagements=()
 # Our list of free males, initially comprised of all of them:
 local freemales=( "${males[@]}" )
 # Now we use the Gale-Shapley algorithm to find a stable set of engagements
 # Loop over the free males. Note that we can't use for..in because the body
 # of the loop may modify the array we're looping over
 local -i m=0
 while (( m < ${#freemales[@]} )); do
   local male=${freemales[m]}
   let m+=1
   # This guy's preferences
   eval 'local his=("${'"$male"'[@]}")'
   # Starting with his favorite
   local -i f=0
   local female=${his[f]}
   # Find her preferences
   eval 'local hers=("${'"$female"'[@]}")'
   # And her current fiancé, if any
   local fiance=${engagements[$female]}
   # If she has a fiancé and prefers him to this guy, look for this guy's next
   # best choice
   while -n $fiance  && 
     (( $(index "$male" "${hers[@]}") > $(index "$fiance" "${hers[@]}") )); do
     let f+=1
     female=${his[f]}
     eval 'hers=("${'"$female"'[@]}")'
     fiance=${engagements[$female]}
   done
   # If we're still on someone who's engaged, it means she prefers this guy
   # to her current fiancé. Dump him and put him at the end of the free list.
   if -n $fiance ; then
     freemales+=("$fiance")
     printf '%-4s rejected %-4s\n' "$female" "$fiance"
   fi
   # We found a match! Record it
   engagements[$female]=$male
   printf '%-4s accepted %-4s\n' "$female" "$male"
 done
 # Display the final result, which should be stable
 print_couples engagements
 # Verify its stability
 print_stable engagements "${females[@]}"
 # Try a swap 
 printf '\nWhat if cath and ivy swap partners?\n'
 local temp=${engagements[cath]}
 engagements[cath]=${engagements[ivy]}
 engagements[ivy]=$temp
 # Display the new result, which should be unstable
 print_couples engagements
 # Verify its instability
 print_stable engagements "${females[@]}"

}

  1. utility function - get index of an item in an array

index() {

 local needle=$1
 shift
 local haystack=("$@")
 local -i i
 for i in "${!haystack[@]}"; do
   if [[ ${haystack[i]} == $needle ]]; then
     printf '%d\n' "$i"
     return 0
   fi
 done
 return 1

}

  1. print the couples from the engagement array; takes name of array as argument

print_couples() {

 printf '\nCouples:\n'
 local keys
 mapfile -t keys < <(eval 'printf '\%s\n'\ "${!'"$1"'[@]}"' | sort)
 local female
 for female in "${keys[@]}"; do
   eval 'local male=${'"$1"'["'"$female"'"]}'
   printf '%-4s is engaged to %-4s\n' "$female" "$male"
 done
 printf '\n'

}

  1. print whether a set of engagements is stable; takes name of engagement array
  2. followed by the list of females

print_stable() {

 if stable "$@"; then
   printf 'These couples are stable.\n'
 else
   printf 'These couples are not stable.\n'
 fi

}

  1. determine if a set of engagements is stable; takes name of engagement array
  2. followed by the list of females

stable() {

 local dict=$1 
 shift
 eval 'local shes=("${!'"$dict"'[@]}")'
 eval 'local hes=("${'"$dict"'[@]}")'
 local -i i
 local -i result=0
 for (( i=0; i<${#shes[@]}; ++i )); do
   local she=${shes[i]} he=${hes[i]}
   eval 'local his=("${'"$he"'[@]}")'
   local alt
   for alt in "$@"; do
     eval 'local fiance=${'"$dict"'["'"$alt"'"]}'
     eval 'local hers=("${'"$alt"'[@]}")'
     if (( $(index "$she" "${his[@]}") > $(index "$alt" "${his[@]}") 
        && $(index "$fiance" "${hers[@]}") > $(index "$he" "${hers[@]}") ))
      then
       printf '%-4s is engaged to %-4s but prefers %4s, ' "$he" "$she" "$alt"
       printf 'while %-4s is engaged to %-4s but prefers %4s.\n' "$alt" "$fiance" "$he"
       result=1
     fi
   done
 done
 if (( result )); then printf '\n'; fi
 return $result

}

main "$@"</lang>

Output:
abi  accepted abe 
cath accepted bob 
hope accepted col 
ivy  accepted dan 
jan  accepted ed  
bea  accepted fred
gay  accepted gav 
eve  accepted hal 
hope rejected col 
hope accepted ian 
abi  rejected abe 
abi  accepted jon 
dee  accepted col 
ivy  rejected dan 
ivy  accepted abe 
fay  accepted dan 

Couples:
abi  is engaged to jon 
bea  is engaged to fred
cath is engaged to bob 
dee  is engaged to col 
eve  is engaged to hal 
fay  is engaged to dan 
gay  is engaged to gav 
hope is engaged to ian 
ivy  is engaged to abe 
jan  is engaged to ed  

These couples are stable.

What if cath and ivy swap partners?

Couples:
abi  is engaged to jon 
bea  is engaged to fred
cath is engaged to abe 
dee  is engaged to col 
eve  is engaged to hal 
fay  is engaged to dan 
gay  is engaged to gav 
hope is engaged to ian 
ivy  is engaged to bob 
jan  is engaged to ed  

bob  is engaged to ivy  but prefers  abi, while abi  is engaged to jon  but prefers  bob.
bob  is engaged to ivy  but prefers  bea, while bea  is engaged to fred but prefers  bob.
bob  is engaged to ivy  but prefers cath, while cath is engaged to abe  but prefers  bob.
bob  is engaged to ivy  but prefers  fay, while fay  is engaged to dan  but prefers  bob.
bob  is engaged to ivy  but prefers hope, while hope is engaged to ian  but prefers  bob.

These couples are not stable.

Ursala

<lang Ursala>men =

{

  'abe': <'abi','eve','cath','ivy','jan','dee','fay','bea','hope','gay'>,
  'bob': <'cath','hope','abi','dee','eve','fay','bea','jan','ivy','gay'>,
  'col': <'hope','eve','abi','dee','bea','fay','ivy','gay','cath','jan'>,
  'dan': <'ivy','fay','dee','gay','hope','eve','jan','bea','cath','abi'>,
  'ed': <'jan','dee','bea','cath','fay','eve','abi','ivy','hope','gay'>,
  'fred': <'bea','abi','dee','gay','eve','ivy','cath','jan','hope','fay'>,
  'gav': <'gay','eve','ivy','bea','cath','abi','dee','hope','jan','fay'>,
  'hal': <'abi','eve','hope','fay','ivy','cath','jan','bea','gay','dee'>,
  'ian': <'hope','cath','dee','gay','bea','abi','fay','ivy','jan','eve'>,
  'jon': <'abi','fay','jan','gay','eve','bea','dee','cath','ivy','hope'>}

women =

{

  'abi': <'bob','fred','jon','gav','ian','abe','dan','ed','col','hal'>,
  'bea': <'bob','abe','col','fred','gav','dan','ian','ed','jon','hal'>,
  'cath': <'fred','bob','ed','gav','hal','col','ian','abe','dan','jon'>,
  'dee': <'fred','jon','col','abe','ian','hal','gav','dan','bob','ed'>,
  'eve': <'jon','hal','fred','dan','abe','gav','col','ed','ian','bob'>,
  'fay': <'bob','abe','ed','ian','jon','dan','fred','gav','col','hal'>,
  'gay': <'jon','gav','hal','fred','bob','abe','col','ed','dan','ian'>,
  'hope': <'gav','jon','bob','abe','ian','dan','hal','ed','col','fred'>,
  'ivy': <'ian','col','hal','gav','fred','bob','abe','ed','jon','dan'>,
  'jan': <'ed','hal','gav','abe','bob','jon','col','ian','fred','dan'>}

match = # finds a stable list of engagements from data as given above

-+

  ^=rrmhPnXS ^/~&l ^/~&rl ^|DlrHSs/~& ^TlK2hlPrSLPAS\~&r -+
     ~&lK2hlPrSXS,
     *=rnmihBPK12D ~&mmhPnXNCB^rnPrmPllSPcA\~&r ~&lrrPwZK17@rnPlX+-,
  ^|rrPlrlPXX/~& ^/~&nNAS ^/~&l+ ^|H\~&+ -:+ * ^|/~& -<+ \/-=+ ~&DSL@tK33+-

preferred = # finds non-couples that would prefer each other to their betrothed

~&lSLPrSLrlXS2c^|DlrHS\~& ~~irlXX+ ^D/~&l+ ^|H\~&+ -:+ *T ^|/~& //~=;+ -~l;+ \/~&H

  1. cast %sWLm

main = # stable, perturbed, and preferred alternatives to the perturbed

<

  'stable': match/men women,
  'perturbed': ~&lSrSxPp match/men women,
  'preferred': preferred/(men,women) ~&lSrSxPp match/men women></lang>

The matches are perturbed by reversing the order of the women.

Output:
<
   'stable': <
      ('jon','abi'),
      ('fred','bea'),
      ('bob','cath'),
      ('col','dee'),
      ('hal','eve'),
      ('dan','fay'),
      ('gav','gay'),
      ('ian','hope'),
      ('abe','ivy'),
      ('ed','jan')>,
   'perturbed': <
      ('jon','jan'),
      ('fred','ivy'),
      ('bob','hope'),
      ('col','gay'),
      ('hal','fay'),
      ('dan','eve'),
      ('gav','dee'),
      ('ian','cath'),
      ('abe','bea'),
      ('ed','abi')>,
   'preferred': <
      ('jon','abi'),
      ('jon','fay'),
      ('fred','abi'),
      ('fred','dee'),
      ('fred','gay'),
      ('fred','eve'),
      ('bob','cath'),
      ('col','dee'),
      ('col','fay'),
      ('col','ivy'),
      ('hal','eve'),
      ('dan','fay'),
      ('gav','gay'),
      ('gav','ivy'),
      ('gav','cath'),
      ('gav','abi'),
      ('abe','abi'),
      ('abe','jan'),
      ('abe','dee'),
      ('abe','fay'),
      ('ed','jan'),
      ('ed','cath'),
      ('ed','fay')>>

VBA

2 methods will be shown here:
1 - using basic VBA-features for strings
2 - using the scripting.dictionary library

The string approach
<lang vb>Sub M_snb()

 c00 = "_abe abi eve cath ivy jan dee fay bea hope gay " & _
       "_bob cath hope abi dee eve fay bea jan ivy gay " & _
       "_col hope eve abi dee bea fay ivy gay cath jan " & _
       "_dan ivy fay dee gay hope eve jan bea cath abi " & _
       "_ed jan dee bea cath fay eve abi ivy hope gay " & _
       "_fred bea abi dee gay eve ivy cath jan hope fay " & _
       "_gav gay eve ivy bea cath abi dee hope jan fay " & _
       "_hal abi eve hope fay ivy cath jan bea gay dee " & _
       "_ian hope cath dee gay bea abi fay ivy jan eve " & _
       "_jon abi fay jan gay eve bea dee cath ivy hope " & _
       "_abi bob fred jon gav ian abe dan ed col hal " & _
       "_bea bob abe col fred gav dan ian ed jon hal " & _
       "_cath fred bob ed gav hal col ian abe dan jon " & _
       "_dee fred jon col abe ian hal gav dan bob ed " & _
       "_eve jon hal fred dan abe gav col ed ian bob " & _
       "_fay bob abe ed ian jon dan fred gav col hal " & _
       "_gay jon gav hal fred bob abe col ed dan ian " & _
       "_hope gav jon bob abe ian dan hal ed col fred " & _
       "_ivy ian col hal gav fred bob abe ed jon dan " & _
       "_jan ed hal gav abe bob jon col ian fred dan "
    
 sn = Filter(Filter(Split(c00), "_"), "-", 0)
 Do
   c01 = Mid(c00, InStr(c00, sn(0) & " "))
   st = Split(Left(c01, InStr(Mid(c01, 2), "_")))
     For j = 1 To UBound(st) - 1
       If InStr(c00, "_" & st(j) & " ") > 0 Then
         c00 = Replace(Replace(c00, sn(0), sn(0) & "-" & st(j)), "_" & st(j), "_" & st(j) & "." & Mid(sn(0), 2))
         Exit For
       Else
         c02 = Filter(Split(c00, "_"), st(j) & ".")(0)
         c03 = Split(Split(c02)(0), ".")(1)
         If InStr(c02, " " & Mid(sn(0), 2) & " ") < InStr(c02, " " & c03 & " ") Then
           c00 = Replace(Replace(Replace(c00, c03 & "-" & st(j), c03), sn(0), sn(0) & "-" & st(j)), "_" & st(j), "_" & st(j) & "." & Mid(sn(0), 2))
           Exit For
         End If
       End If
    Next
    sn = Filter(Filter(Filter(Split(c00), "_"), "-", 0), ".", 0)
  Loop Until UBound(sn) = -1
  
  MsgBox Replace(Join(Filter(Split(c00), "-"), vbLf), "_", "")

End Sub</lang>

The Dictionary approach

<lang vb>Sub M_snb()

 Set d_00 = CreateObject("scripting.dictionary")
 Set d_01 = CreateObject("scripting.dictionary")
 Set d_02 = CreateObject("scripting.dictionary")
  
 sn = Split("abe abi eve cath ivy jan dee fay bea hope gay _" & _
      "bob cath hope abi dee eve fay bea jan ivy gay _" & _
      "col hope eve abi dee bea fay ivy gay cath jan _" & _
      "dan ivy fay dee gay hope eve jan bea cath abi _" & _
      "ed jan dee bea cath fay eve abi ivy hope gay _" & _
      "fred bea abi dee gay eve ivy cath jan hope fay _" & _
      "gav gay eve ivy bea cath abi dee hope jan fay _" & _
      "hal abi eve hope fay ivy cath jan bea gay dee _" & _
      "ian hope cath dee gay bea abi fay ivy jan eve _" & _
      "jon abi fay jan gay eve bea dee cath ivy hope ", "_")

 sp = Split("abi bob fred jon gav ian abe dan ed col hal _" & _
      "bea bob abe col fred gav dan ian ed jon hal _" & _
      "cath fred bob ed gav hal col ian abe dan jon _" & _
      "dee fred jon col abe ian hal gav dan bob ed _" & _
      "eve jon hal fred dan abe gav col ed ian bob _" & _
      "fay bob abe ed ian jon dan fred gav col hal _" & _
      "gay jon gav hal fred bob abe col ed dan ian _" & _
      "hope gav jon bob abe ian dan hal ed col fred _" & _
      "ivy ian col hal gav fred bob abe ed jon dan _" & _
      "jan ed hal gav abe bob jon col ian fred dan ", "_")
    
 For j = 0 To UBound(sn)
   d_00(Split(sn(j))(0)) = ""
   d_01(Split(sp(j))(0)) = ""
   d_02(Split(sn(j))(0)) = sn(j)
   d_02(Split(sp(j))(0)) = sp(j)
 Next
   
 Do
   For Each it In d_00.keys
     If d_00.Item(it) = "" Then
       st = Split(d_02.Item(it))
       For jj = 1 To UBound(st)
         If d_01(st(jj)) = "" Then
           d_00(st(0)) = st(0) & vbTab & st(jj)
           d_01(st(jj)) = st(0)
           Exit For
         ElseIf InStr(d_02.Item(st(jj)), " " & st(0) & " ") < InStr(d_02.Item(st(jj)), " " & d_01(st(jj)) & " ") Then
           d_00(d_01(st(jj))) = ""
           d_00(st(0)) = st(0) & vbTab & st(jj)
           d_01(st(jj)) = st(0)
           Exit For
         End If
       Next
     End If
   Next
 Loop Until UBound(Filter(d_00.items, vbTab)) = d_00.Count - 1
  
 MsgBox Join(d_00.items, vbLf)

End Sub</lang>

Output:
abe  - ivy
bob  - cath
col  - dee
dan  - fay
ed   - jan
fred - bea
gav  - gay
hal  - eve
ian  - hope
jan  - abi

XSLT 2.0

Assume that the input is in XML form as listed here. The following XSLT 2.0 style-sheet...

<lang><xsl:stylesheet version="2.0"

 xmlns:xsl="http://www.w3.org/1999/XSL/Transform" 
 xmlns:fn="http://www.w3.org/2005/xpath-functions" 
 xmlns:xs="http://www.w3.org/2001/XMLSchema" 
 xmlns:m="http://rosettacode.org/wiki/Stable_marriage_problem"
 xmlns:t="http://rosettacode.org/wiki/Stable_marriage_problem/temp" 
 exclude-result-prefixes="xsl xs fn t m">

<xsl:output indent="yes" encoding="UTF-8" omit-xml-declaration="yes" /> <xsl:strip-space elements="*" />

<xsl:template match="*">

 <xsl:copy>
   <xsl:apply-templates select="@*,node()" />
 </xsl:copy>

</xsl:template>

<xsl:template match="@*|comment()|processing-instruction()">

 <xsl:copy />

</xsl:template>

<xsl:template match="m:interest" mode="match-making">

 <m:engagement>
   <m:dude name="{../@name}" /><m:maid name="{.}" />
 </m:engagement>

</xsl:template>

<xsl:template match="m:dude" mode="match-making">

 <xsl:param name="eliminations" select="()" />
 <m:dude name="{@name}">

<xsl:copy-of select="for $b in @name return m:interest[not(. = $eliminations[m:dude/@name=$b]/m:maid/@name)]" />

 </m:dude>

</xsl:template>

<xsl:template match="*" mode="perturbation">

 <xsl:copy>
   <xsl:apply-templates select="@*,node()" mode="perturbation"/>
 </xsl:copy>

</xsl:template>

<xsl:template match="@*" mode="perturbation">

 <xsl:copy />

</xsl:template>

<xsl:template match="m:engagement[position() lt 3]/m:maid/@name" mode="perturbation">

 <xsl:copy-of select="for $c in count(../../preceding-sibling::m:engagement)
      return ../../../m:engagement[2 - $c]/m:maid/@name" />

</xsl:template>

<xsl:template match="m:stable-marriage-problem">

 <xsl:variable name="population" select="m:dude|m:maid" />
 <xsl:variable name="solution">
   <xsl:call-template name="solve-it">
     <xsl:with-param name="dudes" select="m:dude" />
     <xsl:with-param name="maids" select="m:maid" tunnel="yes" /> 
   </xsl:call-template>
 </xsl:variable>
 <xsl:variable name="perturbed">
  <xsl:apply-templates select="$solution/*" mode="perturbation" />
 </xsl:variable>
 <m:stable-marriage-problem-result>
   <m:solution is-stable="{t:is-stable( $population, $solution/*)}">

<xsl:copy-of select="$solution/*" />

   </m:solution>

<m:message>Perturbing the matches! Swapping <xsl:value-of select="$solution/*[1]/m:maid/@name" /> for <xsl:value-of select="$solution/*[2]/m:maid/@name" /></m:message> <m:message><xsl:choose> <xsl:when test="t:is-stable( $population, $perturbed/*)"> <xsl:text>The perturbed configuration is stable.</xsl:text> </xsl:when> <xsl:otherwise>The perturbed configuration is unstable.</xsl:otherwise> </xsl:choose></m:message>

 </m:stable-marriage-problem-result>

</xsl:template>

<xsl:template name="solve-it">

 <xsl:param name="dudes" as="element()*" /> 
 <xsl:param name="maids" as="element()*" tunnel="yes" />  
 <xsl:param name="engagements" as="element()*" select="()" /> 
 
 <xsl:variable name="fresh-proposals">
   <xsl:apply-templates select="$dudes[not(@name = $engagements/m:dude/@name)]/m:interest[1]" mode="match-making" />
 </xsl:variable>
 <xsl:variable name="proposals" select="$engagements | $fresh-proposals/m:engagement" />
 
 <xsl:variable name="acceptable" select="$proposals[
   for $g in m:maid/@name, $b in m:dude/@name, $this-interest in $maids[@name=$g]/m:interest[.=$b]

return every $interest in for $other-b in $proposals[m:maid[@name=$g]]/m:dude/@name[. ne $b] return $maids[@name=$g]/m:interest[.=$other-b] satisfies $interest >> $this-interest

   ]" />
 
 <xsl:variable name="new-dudes">
   <xsl:apply-templates select="$dudes" mode="match-making">
     <xsl:with-param name="eliminations" select="$fresh-proposals/m:engagement" />
   </xsl:apply-templates>
 </xsl:variable>
 
 <xsl:choose>
   <xsl:when test="$dudes[not(for $b in @name return $acceptable[m:dude/@name=$b])]">
 	  <xsl:call-template name="solve-it">
       <xsl:with-param name="dudes" select="$new-dudes/m:dude" />
       <xsl:with-param name="engagements" select="$acceptable" /> 

</xsl:call-template>

   </xsl:when>

<xsl:otherwise>

     <xsl:copy-of select="$acceptable" />

</xsl:otherwise>

 </xsl:choose>

</xsl:template>

<xsl:function name="t:is-stable" as="xs:boolean">

 <xsl:param name="population" as="element()*" />
 <xsl:param name="engagements" as="element()*" />
 <xsl:sequence select="
   every $e in $engagements,

$b in string($e/m:dude/@name), $g in string($e/m:maid/@name), $desired-g in $population/self::m:dude[@name=$b]/m:interest[$g=following-sibling::m:interest], $desired-maid in $population/self::m:maid[@name=$desired-g] satisfies

         not(

$desired-maid/m:interest[.=$b] << $desired-maid/m:interest[.=$engagements[m:maid[@name=$desired-g]]/m:dude/@name])

 " />  

</xsl:function>

</xsl:stylesheet></lang>

...when applied to the said input document will yield...

<lang><t>

  <m:stable-marriage-problem-result xmlns:m="http://rosettacode.org/wiki/Stable_marriage_problem">
     <m:solution is-stable="true">
        <m:engagement>
           <m:dude name="bob"/>
           <m:maid name="cath"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="ed"/>
           <m:maid name="jan"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="fred"/>
           <m:maid name="bea"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="gav"/>
           <m:maid name="gay"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="ian"/>
           <m:maid name="hope"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="jon"/>
           <m:maid name="abi"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="hal"/>
           <m:maid name="eve"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="abe"/>
           <m:maid name="ivy"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="col"/>
           <m:maid name="dee"/>
        </m:engagement>
        <m:engagement>
           <m:dude name="dan"/>
           <m:maid name="fay"/>
        </m:engagement>
     </m:solution>
     <m:message>Perturbing the matches! Swapping cath for jan</m:message>
     <m:message>The perturbed configuration is unstable.</m:message>
  </m:stable-marriage-problem-result>

</t></lang>

zkl

Translation of: PicoLisp

<lang zkl>var

  Boys=Dictionary(
     "abe", "abi eve cath ivy jan dee fay bea hope gay".split(),
     "bob", "cath hope abi dee eve fay bea jan ivy gay".split(),
     "col", "hope eve abi dee bea fay ivy gay cath jan".split(),
     "dan", "ivy fay dee gay hope eve jan bea cath abi".split(),
     "ed",  "jan dee bea cath fay eve abi ivy hope gay".split(),
     "fred","bea abi dee gay eve ivy cath jan hope fay".split(),
     "gav", "gay eve ivy bea cath abi dee hope jan fay".split(),
     "hal", "abi eve hope fay ivy cath jan bea gay dee".split(),
     "ian", "hope cath dee gay bea abi fay ivy jan eve".split(),
     "jon", "abi fay jan gay eve bea dee cath ivy hope".split(), ),
  Girls=Dictionary(
     "abi", "bob fred jon gav ian abe dan ed col hal".split(),
     "bea", "bob abe col fred gav dan ian ed jon hal".split(),
     "cath","fred bob ed gav hal col ian abe dan jon".split(),
     "dee", "fred jon col abe ian hal gav dan bob ed".split(),
     "eve", "jon hal fred dan abe gav col ed ian bob".split(),
     "fay", "bob abe ed ian jon dan fred gav col hal".split(),
     "gay", "jon gav hal fred bob abe col ed dan ian".split(),
     "hope","gav jon bob abe ian dan hal ed col fred".split(),
     "ivy", "ian col hal gav fred bob abe ed jon dan".split(),
     "jan", "ed hal gav abe bob jon col ian fred dan".split(), ),
  Couples=List();  // ( (boy,girl),(boy,girl),...)

Boyz:=Boys.pump(Dictionary(),fcn([(b,gs)]){ return(b,gs.copy()) }); // make writable copy while( bgs:=Boyz.filter1( 'wrap([(Boy,gs)]){ // while unattached boy

            gs and (not Couples.filter1("holds",Boy)) 
    }) )

{

  Boy,Girl:=bgs; Girl=Girl.pop(0);
  Pair:=Couples.filter1("holds",Girl);  // is Girl part of a couple?
  if(not Pair) Couples.append(List(Boy,Girl));	# no, Girl was free
  else{			  // yes, Girl is engaged to Pair[0]
     bsf,nBoy,nB:=Girls[Girl].index, bsf(Boy),bsf(Pair[0]);
     if(nBoy<nB) Pair[0]=Boy;		# Girl prefers Boy, change Couples
  }

} foreach Boy,Girl in (Couples){ println(Girl," is engaged to ",Boy) }

fcn checkCouples(Couples){

  Couples.filter(fcn([(Boy,Girl)]){
     Girls[Girl].filter1('wrap(B){
        // is B before Boy in Girls preferences?
        bsf,nBoy,nB:=Girls[Girl].index, bsf(Boy),bsf(B);

// Does B prefer Girl (over his partner)? _,G:=Couples.filter1("holds",B); // (B,G) gsf,nGirl,nG:=Boys[B].index, gsf(Girl),gsf(G); ( nB<nBoy and nGirl<nG and println(Girl," likes ",B," better than ",Boy," and ",

                   B," likes ",Girl," better than ",G) )
     })
  }) or println("All marriages are stable");

}

checkCouples(Couples); println();

println("Engage fred with abi and jon with bea"); Couples.filter1("holds","fred")[1]="abi"; Couples.filter1("holds","jon") [1]="bea"; checkCouples(Couples);</lang>

Output:
gay is engaged to gav
ivy is engaged to abe
abi is engaged to jon
cath is engaged to bob
hope is engaged to ian
bea is engaged to fred
eve is engaged to hal
fay is engaged to dan
jan is engaged to ed
dee is engaged to col
All marriages are stable

Engage fred with abi and jon with bea
gay likes jon better than gav and jon likes gay better than bea
bea likes fred better than jon and fred likes bea better than abi
eve likes jon better than hal and jon likes eve better than bea
fay likes jon better than dan and jon likes fay better than bea