# Permutations/Derangements

Permutations/Derangements
You are encouraged to solve this task according to the task description, using any language you may know.

A derangement is a permutation of the order of distinct items in which no item appears in its original place.

For example, the only two derangements of the three items (0, 1, 2) are (1, 2, 0), and (2, 0, 1).

The number of derangements of n distinct items is known as the subfactorial of n, sometimes written as !n. There are various ways to calculate !n.

1. Create a named function/method/subroutine/... to generate derangements of the integers 0..n-1, (or 1..n if you prefer).
2. Generate and show all the derangements of 4 integers using the above routine.
3. Create a function that calculates the subfactorial of n, !n.
4. Print and show a table of the counted number of derangements of n vs. the calculated !n for n from 0..9 inclusive.

Optional stretch goal
•   Calculate    !20

## 11l

Translation of: Python
```F derangements(n)
[[Int]] r
V perm = Array(0 .< n)
L
I all(enumerate(perm).map((indx, p) -> indx != p))
r [+]= perm
I !perm.next_permutation()
L.break
R r

F subfact(n) -> Int64
R I n < 2 {1 - n} E (subfact(n - 1) + subfact(n - 2)) * (n - 1)

V n = 4
print(‘Derangements of ’Array(0 .< n))
L(d) derangements(n)
print(‘  ’d)

print("\nTable of n vs counted vs calculated derangements")
L(n) 10
print(‘#2 #<6 #.’.format(n, derangements(n).len, subfact(n)))

n = 20
print("\n!#. = #.".format(n, subfact(n)))```
Output:
```Derangements of [0, 1, 2, 3]
[1, 0, 3, 2]
[1, 2, 3, 0]
[1, 3, 0, 2]
[2, 0, 3, 1]
[2, 3, 0, 1]
[2, 3, 1, 0]
[3, 0, 1, 2]
[3, 2, 0, 1]
[3, 2, 1, 0]

Table of n vs counted vs calculated derangements
0 1      1
1 0      0
2 1      1
3 2      2
4 9      9
5 44     44
6 265    265
7 1854   1854
8 14833  14833
9 133496 133496

!20 = 895014631192902121
```

## 360 Assembly

Translation of: BBC BASIC

Due to 32 bit integers !12 is the limit.

```*        Permutations/Derangements 01/04/2017
DERANGE  CSECT
USING  DERANGE,R13        base register
B      72(R15)            skip savearea
DC     17F'0'             savearea
STM    R14,R12,12(R13)    save previous context
XPRNT  PG1,L'PG1          print title
LA     R1,4               4
LA     R2,1               1 : combinations print
BAL    R14,DERGEN         call dergen
STH    R0,COUNT           count=dergen(4,1)
XPRNT  PG3,L'PG3          print hyphens
SR     R4,R4
STH    R4,II              ii=0
DO WHILE=(CH,R4,LE,=H'9')   do ii=0 to 9
MVC    PG,=CL80' '          clear buffer
XDECO  R4,PG                edit ii
LR     R1,R4                ii
LA     R2,0                 0 : no combination print
BAL    R14,DERGEN           dergen(ii,0)
XDECO  R0,PG+12             edit
LH     R1,II                ii
BAL    R14,SUBFACT          subfact(ii)
XDECO  R0,PG+24             edit
XPRNT  PG,L'PG              print
LH     R4,II                ii
LA     R4,1(R4)             i+1
STH    R4,II                i=i+1
ENDDO    ,                  enddo i
LA     R0,12              12
STH    R0,II              ii=12
MVC    PG,=CL16'!xx='     init buffer
XDECO  R0,XDEC            edit ii
MVC    PG+1(2),XDEC+10    output
LH     R1,II              ii
BAL    R14,SUBFACT        subfact(ii)
XDECO  R0,PG+4            edit subfact(ii)
XPRNT  PG,16              print
L      R13,4(0,R13)       restore previous savearea pointer
LM     R14,R12,12(R13)    restore previous context
XR     R15,R15            rc=0
BR     R14                exit
*------- ----   -------------------------------------------
DERGEN   EQU    *                  dergen(n,fprt)
ST     R14,SAVEDG
ST     R1,N               n
ST     R2,FPRT            fprt
IF LTR,R1,Z,R1 THEN         if n=0 then
LA     R0,1                 1
B      RETDG                return(1)
ENDIF    ,                  endif
MVC    C,=F'0'            c=0
LA     R6,1               i=1
DO WHILE=(C,R6,LE,N)        do i=1 to 2
LR     R1,R6                i
SLA    R1,1
STH    R6,A-2(R1)           a(i)=i
STH    R6,AO-2(R1)          ao(i)=i
LA     R6,1(R6)             i++
ENDDO    ,                  enddo i
L      R1,N               n
BAL    R14,FACT
ST     R0,FACTNM1         fact(n)-1
SR     R6,R6              i=0
DO WHILE=(C,R6,LE,FACTNM1)  do i=0 to fact(n)-1
L      R1,N                 n
BAL    R14,NEXTPER          call nextper(n)
MVI    D,X'01'              d=true
LA     R7,1
DO WHILE=(C,R7,LE,N)          do j=1 to n
LR     R1,R7                  j
SLA    R1,1
LH     R2,A-2(R1)             a(j)
LH     R3,AO-2(R1)            ao(j)
IF CR,R2,EQ,R3 THEN             if a(j)=ao(j) then
MVI    D,X'00'                  d=false
ENDIF    ,                      endif
LA     R7,1(R7)               j++
ENDDO    ,                    enddo j
IF CLI,D,EQ,X'01' THEN        if d then
L      R2,C                   c
LA     R2,1(R2)               c+1
ST     R2,C                   c=c+1
IF CLI,FPRT+3,EQ,X'01' THEN     if fprt=1 then
MVC    PG,=CL80' '              clear buffer
LA     R10,PG                   pgi=0
LA     R7,1                     j=1
DO WHILE=(C,R7,LE,N)              do j=1 to n
LR     R1,R7                      j
SLA    R1,1
LH     R2,A-2(R1)                 a(j)
XDECO  R2,XDEC                    edit
MVC    0(1,R10),XDEC+11           output
LA     R10,2(R10)                 pgi=pgi+2
LA     R7,1(R7)                   j++
ENDDO    ,                        enddo j
XPRNT  PG,L'PG                   print
ENDIF    ,                      endif
ENDIF    ,                    endif
LA     R6,1(R6)             i++
ENDDO    ,                 enddo i
L      R0,C               c
B      RETDG              return(c)
RETDG    L      R14,SAVEDG
BR     R14
SAVEDG   DS     A
*------- ----   -------------------------------------------
NEXTPER  EQU    *                  nextper(nk)
ST     R14,SAVENP
ST     R1,NK              nk
BCTR   R1,0               nk-1
ST     R1,NELEM           nelem=nk-1
IF C,R1,LT,=F'1' THEN       if nelem<1 then
LA     R0,0                 return(0)
B      RETNP
ENDIF    ,                  endif
L      R8,NELEM           nelem
BCTR   R8,0               pos=nelem-1
LOOPW1   EQU    *                  while a(pos+1)>=a(pos+2)
LR     R1,R8                pos
SLA    R1,1
LH     R2,A(R1)             a(pos+1)
CH     R2,A+2(R1)           if a(pos+1)<a(pos+2)
BL     ELOOPW1              then exit while
BCTR   R8,0                 pos=pos-1
IF LTR,R8,M,R8 THEN           if pos<0 then
LA     R1,0                   0
L      R2,NELEM               nelem
BAL    R14,PERMREV            call permrev(0,nelem)
LA     R0,0                   return(0)
B      RETNP
ENDIF    ,                    endif
B      LOOPW1             endwhile
ELOOPW1  L      R9,NELEM           last=nelem
LOOPW2   EQU    *                  do while a(last+1)<=a(pos+1)
LR     R1,R9                last
SLA    R1,1
LH     R2,A(R1)             a(last+1)
LR     R1,R8                pos
SLA    R1,1
CH     R2,A(R1)             if a(last+1)>a(pos+1)
BH     ELOOPW2              then exit while
BCTR   R9,0                 last=last-1
B      LOOPW2             endwhile
ELOOPW2  LR     R1,R8              pos
SLA    R1,1               *2
LA     R2,A(R1)           @a(pos+1)
LR     R1,R9              last
SLA    R1,1
LA     R3,A(R1)           @a(last+1)
LH     R0,0(R2)           w=a(pos+1)
MVC    0(2,R2),0(R3)      a(pos+1)=a(last+1)
STH    R0,0(R3)           a(last+1)=w
LA     R1,1(R8)           pos+1
L      R2,NELEM           nelem
BAL    R14,PERMREV        call permrev(pos+1,nelem)
RETNP    L      R14,SAVENP
BR     R14
SAVENP   DS     A
*------- ----   -------------------------------------------
PERMREV  EQU    *                  permrev(firstix,lastix)
LR     R4,R1              xfirst
LR     R5,R2              xlast
DO WHILE=(CR,R4,LT,R5)      do while(xfirst<xlast)
LR     R1,R4                xfirst
SLA    R1,1                 *2
LA     R2,A(R1)             @a(xfirst+1)
LR     R1,R5                xlast
SLA    R1,1                 *2
LA     R3,A(R1)             @a(xlast+1)
LH     R0,0(R2)             w=a(xfirst+1)
MVC    0(2,R2),0(R3)        a(xfirst+1)=a(xlast+1)
STH    R0,0(R3)             a(xlast+1)=w
LA     R4,1(R4)             xfirst=xfirst+1
BCTR   R5,0                 xlast=xlast-1
ENDDO    ,                  enddo
BR     R14
*------- ----   ----------------------------------------
FACT     EQU    *                  fact(n)
IF C,R1,LE,=F'1' THEN       if n<=1 then
LA     R0,1                 return(1)
ELSE     ,                  else
LA     R5,1                 f=1
LA     R2,1                 i=1
DO WHILE=(CR,R2,LE,R1)        do i=1 to n
MR     R4,R2                  f*i
LA     R2,1(R2)               i++
ENDDO    ,                    enddo
LR     R0,R5                return(f)
ENDIF    ,                  endif
BR     R14
*------- ----   -------------------------------------------
SUBFACT  EQU    *                  subfact(n)
ST     R1,NY              n
IF LTR,R1,Z,R1 THEN         if n=0 then
LA     R0,1                 return(1)
ELSE     ,                  else
LA     R4,1                 1
ST     R4,TT                tt(0)=1
ST     R4,IY                i=1
DO WHILE=(C,R4,LE,NY)         do i=1 to n
L      R4,IY                  i
SRDA   R4,32
D      R4,=F'2'               i/2
IF LTR,R4,Z,R4 THEN             if i//2=0 then
LA     R0,1                     nn=1
ELSE     ,                      else
L      R0,=F'-1'                nn=-1
ENDIF    ,                      endif
L      R1,IY                  i
SLA    R1,2
L      R3,TT-4(R1)            tt(i-1)
M      R2,IY                  *i
AR     R3,R0                  +nn
L      R1,IY                  i
SLA    R1,2
ST     R3,TT(R1)              tt(i)=i*tt(i-1)+nn
L      R4,IY                  i
LA     R4,1(R4)               i++
ST     R4,IY                  i
ENDDO    ,                    enddo
L      R1,NY                n
SLA    R1,2
L      R0,TT(R1)            return(tt(n))
ENDIF    ,                  endif
BR     R14
*        ----   -------------------------------------------
A        DS     12H                A work
AO       DS     12H                A origin
II       DS     H
COUNT    DS     H
N        DS     F
FPRT     DS     F                  flag for printing
C        DS     F
D        DS     X                  boolean : a(i) different ao(i)
FACTNM1  DS     F                  fact(n)-1
NK       DS     F                  n           in nextper
NELEM    DS     F                  n elements  in nextper
NY       DS     F                  n           in subfact
IY       DS     F                  i           in subfact
TT       DS     13F                tt(0:12)
PG1      DC     CL44'derangements for the numbers : 1 2 3 4 are :'
PG2      DC     CL38'  table of n     counted  calculated :'
PG3      DC     CL36' ----------- ----------- -----------'
XDEC     DS     CL12               temp for xdeco
PG       DC     CL80' '            buffer
YREGS
END    DERANGE```
Output:
```derangements for the numbers : 1 2 3 4 are :
2 1 4 3
2 3 4 1
2 4 1 3
3 1 4 2
3 4 1 2
3 4 2 1
4 1 2 3
4 3 1 2
4 3 2 1
table of n     counted  calculated :
----------- ----------- -----------
0           1           1
1           0           0
2           2           1
3           2           2
4           9           9
5          44          44
6         265         265
7        1854        1854
8       14833       14833
9      133496      133496
!12=   176214841
```

## Acornsoft Lisp

Memory limits on machines like the BBC Micro mean that we'd run out of memory if we tried to make a list of all permutations of a list longer than 6 or so elements. Permutations are therefore generated recursively one at a time and given to a visitor function. The recursion is effectively n nested loops for a list of length n and so is not a major obstacle in itself.

```(defun subfact (n)
(cond
((eq n 0) 1)
((eq n 1) 0)
(t (times (sub1 n)
(plus (subfact (sub1 n))
(subfact (sub1 (sub1 n))))))))

(defun count-derangements (n (count . 0))
(visit-derangements (range 1 n)
'(lambda (d) (setq count (add1 count))))
count)

(defun visit-derangements (original-items d-visitor)
(visit-permutations original-items
'(lambda (p)
(cond ((derangement-p original-items p)
(d-visitor p))))))

(defun derangement-p (original d (fail . nil))
(map '(lambda (a b) (cond ((eq a b) (setq fail t))))
original
d)
(not fail))

(defun visit-permutations (items p-visitor)
(visit-permutations-1 items '()))

(defun visit-permutations-1 (items perm)
(cond
((null items) (p-visitor (reverse perm)))
(t
(map '(lambda (i)
(visit-permutations-1
(without i items)
(cons i perm)))
items))))

'(  Utilities  )

(defun without (i items)
(cond ((null items) '())
((eq (car items) i) (cdr items))
(t (cons (car items) (without i (cdr items))))))

(defun reverse (list (result . ()))
(map '(lambda (e) (setq result (cons e result)))
list)
result)

(defun range (from to)
(cond ((greaterp from to) '())
(t (cons from (range (add1 from) to)))))

'(  Examples  )

(defun examples ()
(show-derangements '(1 2 3 4))
(printc)
(map '(lambda (i)
(printc i
'!  (count-derangements i)
'!  (subfact i)))
(range 0 8)))

(defun show-derangements (items)
(printc 'Derangements! of!  items)
(visit-derangements items print))
```
Output:

Calling `(examples)` will output:

```Derangements of (1 2 3 4)
(2 1 4 3)
(2 3 4 1)
(2 4 1 3)
(3 1 4 2)
(3 4 1 2)
(3 4 2 1)
(4 1 2 3)
(4 3 1 2)
(4 3 2 1)

0 1 1
1 0 0
2 1 1
3 2 2
4 9 9
5 44 44
6 265 265
7 1854 1854
8 14833 14833
```

The comparison table stops at n = 8 because, since numbers are 16-bit integers, the program can't count as high as 133496. It can, however, generate all of those derangements.

Translation of: C
```with Ada.Text_IO; use Ada.Text_IO;
procedure DePermute is
type U64 is mod 2**64;
type Num is range 0 .. 20;
type NumList is array (Natural range <>) of Num;
type PtNumList is access all NumList;
package IO is new Ada.Text_IO.Integer_IO (Num);
package UIO is new Ada.Text_IO.Modular_IO (U64);

function deranged (depth : Natural; list : PtNumList;
show : Boolean) return U64 is
tmp : Num;  count : U64 := 0;
begin
if depth = list'Length then
if show then
for i in list'Range loop IO.Put (list (i), 2); end loop;
New_Line;
end if;  return 1;
end if;
for i in reverse depth .. list'Last loop
if Num (i + 1) /= list (depth) then
tmp := list (i); list (i) := list (depth); list (depth) := tmp;
count := count + deranged (depth + 1, list, show);
tmp := list (i); list (i) := list (depth); list (depth) := tmp;
end if;
end loop;
return count;
end deranged;

function gen_n (len : Natural; show : Boolean) return U64 is
list : PtNumList;
begin
list := new NumList (0 .. len - 1);
for i in list'Range loop list (i) := Num (i + 1); end loop;
return deranged (0, list, show);
end gen_n;

function sub_fact (n : Natural) return U64 is begin
if n < 2 then return U64 (1 - n);
else return (sub_fact (n - 1) + sub_fact (n - 2)) * U64 (n - 1);
end if;
end sub_fact;

count : U64;
begin
Put_Line ("Deranged 4:");
count := gen_n (4, True);
Put_Line ("List vs. calc:");
for i in Natural range 0 .. 9 loop
IO.Put (Num (i), 1);  UIO.Put (gen_n (i, False), 7);
UIO.Put (sub_fact (i), 7);  New_Line;
end loop;
Put_Line ("!20 = " & U64'Image (sub_fact (20)));
end DePermute;
```
Output:
```Deranged 4:
4 1 2 3
4 3 1 2
4 3 2 1
3 4 2 1
3 4 1 2
3 1 4 2
2 4 1 3
2 3 4 1
2 1 4 3
List vs. calc:
0      1      1
1      0      0
2      1      1
3      2      2
4      9      9
5     44     44
6    265    265
7   1854   1854
8  14833  14833
9 133496 133496
!20 =  895014631192902121```

## Arturo

```isClean?: function [s,o][
loop.with:'i s 'a [
if a = o\[i] -> return false
]
return true
]

derangements: function [n][
original: 1..n
select permutate original 'x ->
isClean? x original
]

subfactorial: function [n].memoize[
(n =< 1)? -> 1 - n
-> (n-1) * (add subfactorial n-1 subfactorial n-2)
]

print "Derangements of 1 2 3 4:"
loop derangements 4 'x [
print x
]

print "\nNumber of derangements:"
print repeat "-" 39
loop 0..9 'z [
counted: size derangements z
calculated: subfactorial z
]

print ~"\n!20 = |subfactorial 20|"
```
Output:
```Derangements of 1 2 3 4:
4 1 2 3
3 1 4 2
3 4 1 2
4 3 1 2
2 1 4 3
2 4 1 3
2 3 4 1
3 4 2 1
4 3 2 1

Number of derangements:
n         counted      calculated
---------------------------------------
0               1               1
1               0               0
2               1               1
3               2               2
4               9               9
5              44              44
6             265             265
7            1854            1854
8           14833           14833
9          133496          133496

!20 = 895014631192902121```

## AutoHotkey

Works with: AutoHotkey_L

Note that the permutations are generated in lexicographic order, from http://www.autohotkey.com/forum/topic77959.html

```#NoEnv
SetBatchLines -1
Process, Priority,, high

output := "Derangements for 1, 2, 3, 4:`n"

obj := [1, 2, 3, 4], objS := obj.Clone()
Loop ; permute 4
{
obj := perm_NextObj(Obj)
If !obj
break
For k, v in obj
if ( objS[k] = v )
continue 2
output .= ObjDisp(obj) "`n"
}
output .= "`nTable of n, counted, calculated derangements:`n"

Loop 10 ; Count !n
{
obj := []
count := 0
output .= A_Tab . (i := A_Index-1) . A_Tab
Loop % i
obj[A_Index] := A_Index
objS := obj.Clone()
Loop
{
obj := perm_NextObj(Obj)
If !obj
break
For k, v in obj
if ( objS[k] = v )
continue 2
count++
}
output .= count . A_Tab . cd(i) . "`n"
}
output .= "`nApproximation of !20: " . cd(20)
MsgBox % Clipboard := output

perm_NextObj(obj){ ; next lexicographic permutation
p := 0, objM := ObjMaxIndex(obj)
Loop % objM
{
If A_Index=1
continue
t := obj[objM+1-A_Index]
n := obj[objM+2-A_Index]
If ( t < n )
{
p := objM+1-A_Index, pC := obj[p]
break
}
}
If !p
return false
Loop
{
t := obj[objM+1-A_Index]
If ( t > pC )
{
n := objM+1-A_Index, nC := obj[n]
break
}
}

obj[n] := pC, obj[p] := nC
return ObjReverse(obj, objM-p)
}

ObjReverse(Obj, tail){
o := ObjClone(Obj), ObjM := ObjMaxIndex(O)
Loop % tail
o[ObjM-A_Index+1] := Obj[ObjM+A_Index-tail]
return o
}

ObjDisp(obj){
For k, v in obj
s .= v ", "
return SubStr(s, 1, strLen(s)-2)
}

cd(n){  ; Count Derangements
static e := 2.71828182845904523536028747135
return n ? floor(ft(n)/e + 1/2) : 1
}
ft(n){  ; FacTorial
a := 1
Loop % n
a *= A_Index
return a
}
```
Output:
```Derangements for 1, 2, 3, 4:
2, 1, 4, 3
2, 3, 4, 1
2, 4, 1, 3
3, 1, 4, 2
3, 4, 1, 2
3, 4, 2, 1
4, 1, 2, 3
4, 3, 1, 2
4, 3, 2, 1

Table of n, counted, calculated derangements:
0	0	1
1	0	0
2	1	1
3	2	2
4	9	9
5	44	44
6	265	265
7	1854	1854
8	14833	14833
9	133496	133496

Approximation of !20: 895014631192902144```

## BBC BASIC

```      PRINT"Derangements for the numbers 0,1,2,3 are:"
Count% = FN_Derangement_Generate(4,TRUE)

PRINT'"Table of n, counted derangements, calculated derangements :"

FOR I% = 0 TO 9
PRINT I%, FN_Derangement_Generate(I%,FALSE), FN_SubFactorial(I%)
NEXT

PRINT'"There is no long int in BBC BASIC!"
PRINT"!20 = ";FN_SubFactorial(20)

END

DEF FN_Derangement_Generate(N%, fPrintOut)
LOCAL A%(), O%(), C%, D%, I%, J%
IF N% = 0 THEN = 1
DIM A%(N%-1), O%(N%-1)
FOR I% = 0 TO N%-1 : A%(I%) = I% : NEXT
O%() = A%()
FOR I% = 0 TO FN_Factorial(DIM(A%(),1)+1)-1
PROC_NextPermutation(A%())
D% = TRUE
FOR J%=0 TO N%-1
IF A%(J%) = O%(J%) THEN D% = FALSE
NEXT
IF D% THEN
C% += 1
IF fPrintOut THEN
FOR K% = 0 TO N%-1
PRINT ;A%(K%);" ";
NEXT
PRINT
ENDIF
ENDIF
NEXT
= C%

DEF PROC_NextPermutation(A%())
LOCAL first, last, elementcount, pos
elementcount = DIM(A%(),1)
IF elementcount < 1 THEN ENDPROC
pos = elementcount-1
WHILE A%(pos) >= A%(pos+1)
pos -= 1
IF pos < 0 THEN
PROC_Permutation_Reverse(A%(), 0, elementcount)
ENDPROC
ENDIF
ENDWHILE
last = elementcount
WHILE A%(last) <= A%(pos)
last -= 1
ENDWHILE
SWAP A%(pos), A%(last)
PROC_Permutation_Reverse(A%(), pos+1, elementcount)
ENDPROC

DEF PROC_Permutation_Reverse(A%(), firstindex, lastindex)
LOCAL first, last
first = firstindex
last = lastindex
WHILE first < last
SWAP A%(first), A%(last)
first += 1
last -= 1
ENDWHILE
ENDPROC

DEF FN_Factorial(N) : IF (N = 1) OR (N = 0) THEN =1 ELSE = N * FN_Factorial(N-1)

DEF FN_SubFactorial(N) : IF N=0 THEN =1 ELSE =N*FN_SubFactorial(N-1)+-1^N

REM Or you could use:
REM DEF FN_SubFactorial(N) : IF N<1 THEN =1 ELSE =(N-1)*(FN_SubFactorial(N-1)+FN_SubFactorial(N-2))```
Output:
```Derangements for the numbers 0,1,2,3 are:
1 0 3 2
1 2 3 0
1 3 0 2
2 0 3 1
2 3 0 1
2 3 1 0
3 0 1 2
3 2 0 1
3 2 1 0

Table of n, counted derangements, calculated derangements :
0         1         1
1         0         0
2         1         1
3         2         2
4         9         9
5        44        44
6       265       265
7      1854      1854
8     14833     14833
9    133496    133496

There is no long int in BBC BASIC!
!20 = 8.95014632E17
>```

## Bracmat

The function `calculated-!n` has a local variable `mem` that memoizes already found counts. This is done by actually updating the function's definition. The output of the expression `lst\$calculated-!n` demonstrates this.

The function `counted-!n` is also special: it is designed to always fail, forcing the match operation on the subject `!H` to assign each element in `!H` in turn to the sub-pattern `(%@?h:~!p)`, except the element that is equal to `!p`. The derangements are built up in the last argument and accumulated in the global variable `D`. Also the counter `count` is a global variable.

```( ( calculated-!n
=   memo answ
.   (memo==)
& ( !arg:0&1
| !arg:1&0
| !(memo.):? (!arg.?answ) ?&!answ
|       (!arg+-1)
* (calculated-!n\$(!arg+-1)+calculated-!n\$(!arg+-2))
: ?answ
& (!arg.!answ) !(memo.):?(memo.)
& !answ
)
)
& ( counted-!n
=   p P h H A Z L
.     !arg:(%?p ?P.?H.?L)
&   !H
:   ?A
(%@?h:~!p)
(?Z&counted-!n\$(!P.!A !Z.!h !L))
|   !arg:(..?L)
& 1+!count:?count
& (!count.!L) !D:?D
& ~
)
& out\$"Derangements of 1 2 3 4"
& :?D
& 0:?count
& ( counted-!n\$(4 3 2 1.4 3 2 1.)
| out\$!D
)
=   len w
.   @(!arg:? [?len)
& @("       ":? [!len ?w)
& !w !arg
)
& :?K
& -1:?N
&   whl
' ( !N+1:<10:?N
& (   0:?count
& :?D
& counted-!n\$(!K.!K.)
)
& !N !K:?K
)
& out\$("!20 =" calculated-!n\$20)
& lst\$calculated-!n
)```
Output:
```Derangements of 1 2 3 4
(9.4 3 2 1)
(8.3 4 2 1)
(7.2 3 4 1)
(6.4 3 1 2)
(5.3 4 1 2)
(4.3 1 4 2)
(3.2 4 1 3)
(2.4 1 2 3)
(1.2 1 4 3)
N   List   Calc
0      1      1
1      0      0
2      1      1
3      2      2
4      9      9
5     44     44
6    265    265
7   1854   1854
8  14833  14833
9 133496 133496
!20 = 895014631192902121
(calculated-!n=
memo answ
.   ( memo
=
=   (20.895014631192902121)
(19.44750731559645106)
(18.2355301661033953)
(17.130850092279664)
(16.7697064251745)
(15.481066515734)
(14.32071101049)
(13.2290792932)
(12.176214841)
(11.14684570)
(10.1334961)
(9.133496)
(8.14833)
(7.1854)
(6.265)
(5.44)
(4.9)
(3.2)
(2.1)
)
& ( !arg:0&1
| !arg:1&0
| !(memo.):? (!arg.?answ) ?&!answ
|     (!arg+-1)*(calculated-!n\$(!arg+-1)+calculated-!n\$(!arg+-2))
: ?answ
& (!arg.!answ) !(memo.):?(memo.)
& !answ
)
);```

## C

```#include <stdio.h>
typedef unsigned long long LONG;

LONG deranged(int depth, int len, int *d, int show)
{
int i;
char tmp;
LONG count = 0;

if (depth == len) {
if (show) {
for (i = 0; i < len; i++) putchar(d[i] + 'a');
putchar('\n');
}
return 1;
}
for (i = len - 1; i >= depth; i--) {
if (i == d[depth]) continue;

tmp = d[i]; d[i] = d[depth]; d[depth] = tmp;
count += deranged(depth + 1, len, d, show);
tmp = d[i]; d[i] = d[depth]; d[depth] = tmp;
}
return count;
}

LONG gen_n(int n, int show)
{
LONG i;
int a[1024]; /* 1024 ought to be big enough for anybody */

for (i = 0; i < n; i++) a[i] = i;
return deranged(0, n, a, show);
}

LONG sub_fact(int n)
{
return n < 2 ? 1 - n : (sub_fact(n - 1) + sub_fact(n - 2)) * (n - 1);
}

int main()
{
int i;

printf("Deranged Four:\n");
gen_n(4, 1);

printf("\nCompare list vs calc:\n");
for (i = 0; i < 10; i++)
printf("%d:\t%llu\t%llu\n", i, gen_n(i, 0), sub_fact(i));

printf("\nfurther calc:\n");
for (i = 10; i <= 20; i++)
printf("%d: %llu\n", i, sub_fact(i));

return 0;
}
```
Output:
```Deranged Four:
dabc
dcab
dcba
cdba
cdab
bdac
bcda

Compare list vs calc:
0:      1       1
1:      0       0
2:      1       1
3:      2       2
4:      9       9
5:      44      44
6:      265     265
7:      1854    1854
8:      14833   14833
9:      133496  133496

further calc:
10: 1334961
11: 14684570
12: 176214841
13: 2290792932
14: 32071101049
15: 481066515734
16: 7697064251745
17: 130850092279664
18: 2355301661033953
19: 44750731559645106
20: 895014631192902121```

## C#

Recursive version

```using System;
class Derangements
{
static int n = 4;
static int [] buf = new int [n];
static bool [] used = new bool [n];

static void Main()
{
for (int i = 0; i < n; i++) used [i] = false;
rec(0);
}

static void rec(int ind)
{
for (int i = 0; i < n; i++)
{
if (!used [i] && i != ind)
{
used [i] = true;
buf [ind] = i;
if (ind + 1 < n) rec(ind + 1);
else Console.WriteLine(string.Join(",", buf));
used [i] = false;
}
}
}
}
```

## C++

```#include <cstdint>
#include <iomanip>
#include <iostream>
#include <numeric>
#include <vector>

typedef std::pair<std::vector<std::vector<int32_t>>, int32_t> list_or_count;

uint64_t factorial(const int32_t& n) {
uint64_t result = 1;
for ( int32_t i = 2; i <= n; ++i ) {
result *= i;
}
return result;
}

uint64_t subfactorial(const int32_t& n) {
if ( n >= 0 && n <= 2 ) {
return ( n == 1 ) ? 0 : 1;
}
return ( n - 1 ) * ( subfactorial(n - 1) + subfactorial(n - 2) );
}

list_or_count derangements(const int32_t& n, const bool& count_only) {
std::vector<int32_t> sequence(n, 0);
std::iota(sequence.begin() ,sequence.end(), 1);
std::vector<int32_t> original(sequence);
uint64_t permutation_count = factorial(n);

std::vector<std::vector<int32_t>> list;
int32_t count = ( n == 0 ) ? 1 : 0;

while ( --permutation_count > 0 ) {
int32_t j = n - 2;
while ( sequence[j] > sequence[j + 1] ) {
j--;
}
int32_t k = n - 1;
while ( sequence[j] > sequence[k] ) {
k--;
}
std::swap(sequence[j], sequence[k]);

int32_t r = n - 1;
int32_t s = j + 1;
while ( r > s ) {
std::swap(sequence[r], sequence[s]);
r--;
s++;
}

j = 0;
while ( j < n && sequence[j] != original[j] ) {
j++;
}
if ( j == n ) {
if ( count_only ) {
count++;
} else {
std::vector<int32_t> copy_sequence(sequence);
list.emplace_back(copy_sequence);
}
}
}
return list_or_count(list, count);
}

int main() {
std::cout << "Derangements for n = 4" << std::endl;
list_or_count list_count = derangements(4, false);
for ( std::vector<int32_t> list : list_count.first ) {
std::cout << "[";
for ( uint64_t i = 0; i < list.size() - 1; ++i ) {
std::cout << list[i] << ", ";
}
std::cout << list.back() << "]" << std::endl;
}
std::cout << std::endl;

std::cout << "n   derangements      !n" << std::endl;
std::cout << "------------------------" << std::endl;
for ( int32_t n = 0; n < 10; ++n ) {
int32_t count = derangements(n, true).second;
std::cout << n << ":  " << std::setw(9) << count << "  " << std::setw(9) << subfactorial(n) << std::endl;
}
std::cout << std::endl;

std::cout << "!20 = " << subfactorial(20) << std::endl;
}
```
Output:
```Derangements for n = 4
[2, 1, 4, 3]
[2, 3, 4, 1]
[2, 4, 1, 3]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 3, 1, 2]
[4, 3, 2, 1]

n   derangements      !n
------------------------
0:          1          1
1:          0          0
2:          1          1
3:          2          2
4:          9          9
5:         44         44
6:        265        265
7:       1854       1854
8:      14833      14833
9:     133496     133496

!20 = 895014631192902121
```

## Clojure

Generating functions with no fixed point

```(ns derangements.core
(:require [clojure.set :as s]))

(defn subfactorial [n]
(case n
0 1
1 0
(* (dec n) (+ (subfactorial (dec n)) (subfactorial (- n 2))))))

(defn no-fixed-point
"f : A -> B must be a biyective function written as a hash-map, returns
all g : A -> B such that (f(a) = b) => not(g(a) = b)"
[f]
(case (count f)
0 [{}]
1 []
(let [g  (s/map-invert f)
a  (first (keys f))
a' (f a)]
(mapcat
(fn [b'] (let [b  (g b')
f' (dissoc f a b)]
(concat (map #(reduce conj % [[a b'] [b a']])
(no-fixed-point f'))
(map #(conj % [a b'])
(no-fixed-point (assoc f' b a'))))))
(filter #(not= a' %) (keys g))))))

(defn derangements [xs]
{:pre [(= (count xs) (count (set xs)))]}
(map (fn [f] (mapv f xs))
(no-fixed-point (into {} (map vector xs xs)))))

(defn -main []
(do
(doall (map println (derangements [0,1,2,3])))
(doall (map #(println (str (subfactorial %) " " (count (derangements (range %)))))
(range 10)))
(println (subfactorial 20))))
```
Output:
```[1 0 3 2]
[1 2 3 0]
[1 3 0 2]
[2 3 0 1]
[2 3 1 0]
[2 0 3 1]
[3 2 1 0]
[3 2 0 1]
[3 0 1 2]
1 1
0 0
1 1
2 2
9 9
44 44
265 265
1854 1854
14833 14833
133496 133496
895014631192902121```

## Common Lisp

Translation of: Acornsoft Lisp
```(defun subfact (n)
(cond
((= n 0) 1)
((= n 1) 0)
(t (* (- n 1)
(+ (subfact (- n 1))
(subfact (- n 2)))))))

(defun count-derangements (n)
(let ((count 0))
(visit-derangements (range 1 n)
(lambda (d) (declare (ignore d)) (incf count)))
count))

(defun visit-derangements (items visitor)
(visit-permutations items
(lambda (p)
(when (derangement-p items p)
(funcall visitor p)))))

(defun derangement-p (original d)
(notany #'equal original d))

(defun visit-permutations (items visitor)
(labels
((vp (items perm)
(cond ((null items)
(funcall visitor (reverse perm)))
(t
(mapc (lambda (i)
(vp (remove i items)
(cons i perm)))
items)))))
(vp items '())))

(defun range (start end)
(loop for i from start to end collect i))

(defun examples ()
(show-derangements '(1 2 3 4))
(format t "~%n  counted     !n~%")
(dotimes (i 10)
(format t "~S ~7@S ~7@S~%"
i
(count-derangements i)
(subfact i)))
(format t "~%!20 = ~S~2%" (subfact 20)))

(defun show-derangements (items)
(format t "~%Derangements of ~S~%" items)
(visit-derangements items
(lambda (d)
(format t "  ~S~%" d))))
```
Output:

Calling `(examples)` would output:

```Derangements of (1 2 3 4)
(2 1 4 3)
(2 3 4 1)
(2 4 1 3)
(3 1 4 2)
(3 4 1 2)
(3 4 2 1)
(4 1 2 3)
(4 3 1 2)
(4 3 2 1)

n  counted     !n
0       1       1
1       0       0
2       1       1
3       2       2
4       9       9
5      44      44
6     265     265
7    1854    1854
8   14833   14833
9  133496  133496

!20 = 895014631192902121
```

## D

### Iterative Version

```import std.stdio, std.algorithm, std.typecons, std.conv,
std.range, std.traits;

T factorial(T)(in T n) pure nothrow @safe @nogc {
Unqual!T result = 1;
foreach (immutable i; 2 .. n + 1)
result *= i;
return result;
}

T subfact(T)(in T n) pure nothrow @safe @nogc {
if (0 <= n && n <= 2)
return n != 1;
return (n - 1) * (subfact(n - 1) + subfact(n - 2));
}

auto derangements(in size_t n, in bool countOnly=false)
pure nothrow @safe {
size_t[] seq = n.iota.array;
auto ori = seq.idup;
size_t[][] all;
size_t cnt = n == 0;

foreach (immutable tot; 0 .. n.factorial - 1) {
size_t j = n - 2;
while (seq[j] > seq[j + 1])
j--;
size_t k = n - 1;
while (seq[j] > seq[k])
k--;
seq[k].swap(seq[j]);

size_t r = n - 1;
size_t s = j + 1;
while (r > s) {
seq[s].swap(seq[r]);
r--;
s++;
}

j = 0;
while (j < n && seq[j] != ori[j])
j++;
if (j == n) {
if (countOnly)
cnt++;
else
all ~= seq.dup;
}
}

return tuple(all, cnt);
}

void main() @safe {
"Derangements for n = 4:".writeln;
foreach (const d; 4.derangements[0])
d.writeln;

"\nTable of n vs counted vs calculated derangements:".writeln;
foreach (immutable i; 0 .. 10)
writefln("%s  %-7s%-7s", i, derangements(i, 1)[1], i.subfact);

writefln("\n!20 = %s", 20L.subfact);
}
```
Output:
```Derangements for n = 4:
[1, 0, 3, 2]
[1, 2, 3, 0]
[1, 3, 0, 2]
[2, 0, 3, 1]
[2, 3, 0, 1]
[2, 3, 1, 0]
[3, 0, 1, 2]
[3, 2, 0, 1]
[3, 2, 1, 0]

Table of n vs counted vs calculated derangements:
0  1      1
1  0      0
2  1      1
3  2      2
4  9      9
5  44     44
6  265    265
7  1854   1854
8  14833  14833
9  133496 133496

!20 = 895014631192902121```

### Recursive Version

Slightly slower but more compact recursive version of the derangements function, based on the D entry of the permutations task. Same output.

```import std.stdio, std.algorithm, std.typecons, std.conv, std.range;

T factorial(T)(in T n) pure nothrow {
Unqual!T result = 1;
foreach (immutable i; 2 .. n + 1)
result *= i;
return result;
}

T subfact(T)(in T n) pure nothrow {
if (0 <= n && n <= 2)
return n != 1;
return (n - 1) * (subfact(n - 1) + subfact(n - 2));
}

auto derangementsR(in size_t n, in bool countOnly=false) pure
/*nothrow*/ {
auto seq = n.iota.array;
immutable ori = seq.idup;
const(size_t[])[] res;
size_t cnt;

void perms(in size_t[] s, in size_t[] pre=null) /*nothrow*/ {
if (s.length) {
foreach (immutable i, immutable c; s)
perms(s[0 .. i] ~ s[i + 1 .. \$], pre ~ c);
} else if (zip(pre, ori).all!(po => po[0] != po[1])) {
if (countOnly) cnt++;
else res ~= pre;
}
}

perms(seq);
return tuple(res, cnt);
}

void main() {
"Derangements for n = 4:".writeln;
foreach (const d; 4.derangementsR[0])
d.writeln;

"\nTable of n vs counted vs calculated derangements:".writeln;
foreach (immutable i; 0 .. 10)
writefln("%s  %-7s%-7s", i, derangementsR(i, 1)[1], i.subfact);

writefln("\n!20 = %s", 20L.subfact);
}
```

## EasyLang

```global list[] rlist[][] .
proc permlist k . .
if k >= len list[]
for i to len list[]
if i = list[i]
return
.
.
rlist[][] &= list[]
return
.
for i = k to len list[]
swap list[i] list[k]
permlist k + 1
swap list[k] list[i]
.
.
#
proc derang n . r[][] .
rlist[][] = [ ]
list[] = [ ]
for i to n
list[] &= i
.
permlist 1
r[][] = rlist[][]
.
r[][] = [ ]
derang 4 r[][]
print r[][]
#
func subfac n .
if n < 2
return 1 - n
.
return (subfac (n - 1) + subfac (n - 2)) * (n - 1)
.
#
print "counted / calculated"
for n = 0 to 9
derang n r[][]
print n & ": " & len r[][] & " " & subfac n
.```

## EchoLisp

```(lib 'list) ;; in-permutations
(lib 'bigint)

;; generates derangements by filtering out permutations
(define (derangement? nums) ;; predicate
(for/and ((n nums) (i (length nums))) (!= n i)))

(define (derangements n)
(for/list ((p (in-permutations n))) #:when (derangement? p) p))

(define (count-derangements n)
(for/sum ((p (in-permutations n))) #:when (derangement? p) 1))

;;
;;  !n = (n - 1) (!(n-1) + !(n-2))

(define (!n n)
(* (1- n) (+ (!n (1- n)) (!n (- n 2)))))
(remember '!n #(1 0))
```
Output:
```(derangements 4)
→ ((3 0 1 2) (2 0 3 1) (2 3 0 1) (3 2 0 1) (3 2 1 0) (2 3 1 0) (1 2 3 0) (1 3 0 2) (1 0 3 2))

;; generated versus computed

(for ((i 10)) (writeln i '| (count-derangements i) (!n i)))

0     |     1     1
1     |     0     0
2     |     1     1
3     |     2     2
4     |     9     9
5     |     44     44
6     |     265     265
7     |     1854     1854
8     |     14833     14833
9     |     133496     133496

(!n 20)
→ 895014631192902121
```

## Elixir

Translation of: Ruby
```defmodule Permutation do
def derangements(n) do
list = Enum.to_list(1..n)
Enum.filter(permutation(list), fn perm ->
Enum.zip(list, perm) |> Enum.all?(fn {a,b} -> a != b end)
end)
end

def subfact(0), do: 1
def subfact(1), do: 0
def subfact(n), do: (n-1) * (subfact(n-1) + subfact(n-2))

def permutation([]), do: [[]]
def permutation(list) do
for x <- list, y <- permutation(list -- [x]), do: [x|y]
end
end

IO.puts "derangements for n = 4"
Enum.each(Permutation.derangements(4), &IO.inspect &1)

IO.puts "\nNumber of derangements"
IO.puts " n    derange   subfact"
Enum.each(0..9, fn n ->
:io.format "~2w :~9w,~9w~n", [n, length(Permutation.derangements(n)), Permutation.subfact(n)]
end)
Enum.each(10..20, fn n ->
:io.format "~2w :~19w~n", [n, Permutation.subfact(n)]
end)
```
Output:
```derangements for n = 4
[2, 1, 4, 3]
[2, 3, 4, 1]
[2, 4, 1, 3]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 3, 1, 2]
[4, 3, 2, 1]

Number of derangements
n    derange   subfact
0 :        1,        1
1 :        0,        0
2 :        1,        1
3 :        2,        2
4 :        9,        9
5 :       44,       44
6 :      265,      265
7 :     1854,     1854
8 :    14833,    14833
9 :   133496,   133496
10 :            1334961
11 :           14684570
12 :          176214841
13 :         2290792932
14 :        32071101049
15 :       481066515734
16 :      7697064251745
17 :    130850092279664
18 :   2355301661033953
19 :  44750731559645106
20 : 895014631192902121
```

## F#

### The Function

```// Generate derangements. Nigel Galloway: July 9th., 2019
let derange n=
let fG n i g=let e=Array.copy n in e.[i]<-n.[g]; e.[g]<-n.[i]; e
let rec derange n g α=seq{
match (α>0,n&&&(1<<<α)=0) with
(true,true)->for i in [0..α-1] do if n&&&(1<<<i)=0 then let g=(fG g α i) in yield! derange (n+(1<<<i)) g (α-1); yield! derange n g (α-1)
|(true,false)->yield! derange n g (α-1)
|(false,false)->yield g
|_->()}
derange 0 [|1..n|] (n-1)
```

```derange 4 |> Seq.iter(printfn "%A")
```
Output:
```[|4; 3; 2; 1|]
[|2; 3; 4; 1|]
[|3; 4; 2; 1|]
[|3; 4; 1; 2|]
[|4; 3; 1; 2|]
[|3; 1; 4; 2|]
[|2; 1; 4; 3|]
[|2; 4; 1; 3|]
[|4; 1; 2; 3|]
```
```let subFact n=let rec fN n g=match n with 0m->int64(round(g/2.7182818284590452353602874713526624978m))|_->fN (n-1m) (g*n) in if n=0 then 1L else fN (decimal n) 1m
[1..9] |> Seq.iter(fun n->printfn "items=%d !n=%d derangements=%d" n (subFact n) (derange n|>Seq.length))
```
Output:
```items=1 !n=0 derangements=0
items=2 !n=1 derangements=1
items=3 !n=2 derangements=2
items=4 !n=9 derangements=9
items=5 !n=44 derangements=44
items=6 !n=265 derangements=265
items=7 !n=1854 derangements=1854
items=8 !n=14833 derangements=14833
items=9 !n=133496 derangements=133496
```

## Factor

Works with: Factor version 0.98
```USING: combinators formatting io kernel math math.combinatorics
prettyprint sequences ;
IN: rosetta-code.derangements

: !n ( n -- m )
{
{ 0 [ 1 ] }
{ 1 [ 0 ] }
[ [ 1 - !n ] [ 2 - !n + ] [ 1 - * ] tri ]
} case ;

: derangements ( n -- seq )
<iota> dup [ [ = ] 2map [ f = ] all? ] with
filter-permutations ;

"4 derangements" print 4 derangements . nl
"n   count    calc\n=  ======  ======" print
10 <iota> [
dup [ derangements length ] [ !n ] bi
"%d%8d%8d\n" printf
] each nl
"!20 = " write 20 !n .
```
Output:
```4 derangements
V{
{ 1 0 3 2 }
{ 1 2 3 0 }
{ 1 3 0 2 }
{ 2 0 3 1 }
{ 2 3 0 1 }
{ 2 3 1 0 }
{ 3 0 1 2 }
{ 3 2 0 1 }
{ 3 2 1 0 }
}

n   count    calc
=  ======  ======
0       1       1
1       0       0
2       1       1
3       2       2
4       9       9
5      44      44
6     265     265
7    1854    1854
8   14833   14833
9  133496  133496

!20 = 895014631192902121
```

## FreeBASIC

```' version 08-04-2017
' compile with: fbc -s console

Sub Subfactorial(a() As ULongInt)

Dim As ULong i
Dim As ULongInt num

For i = 0 To UBound(a)
num = num * i
If (i And 1) = 1 Then
num -= 1
Else
num += 1
End If
a(i) = num
Next

End Sub

' Heap's algorithm non-recursive
Function perms_derange(n As ULong, flag As Long = 0) As ULongInt
' fast upto n < 12
If n = 0 Then Return 1

Dim As ULong i, j, c1, count
Dim As ULong a(0 To n -1), c(0 To n -1)

For j = 0 To n -1
a(j) = j
Next

While i < n
If c(i) < i Then
If (i And 1) = 0 Then
Swap a(0), a(i)
Else
Swap a(c(i)), a(i)
End If
For j = 0 To n -1
If a(j) = j Then j = 99
Next
If j < 99 Then
count += 1
If flag = 0 Then
c1 += 1
For j = 0 To n -1
Print a(j);
Next
If c1 > 12 Then
Print : c1 = 0
Else
Print " ";
End If
End If
End If
c(i) += 1
i = 0
Else
c(i) = 0
i += 1
End If
Wend
If flag = 0 AndAlso c1 <> 0 Then Print
Return count

End Function

' ------=< MAIN >=------

Dim As ULong i, n = 4
Dim As ULongInt subfac(20)

Subfactorial(subfac())

Print "permutations derangements for n = "; n
i = perms_derange(n)
Print "count returned = "; i; " , !"; n; " calculated = "; subfac(n)

Print
Print "count  counted subfactorial"
Print "---------------------------"
For i = 0 To 9
Print Using " ###: ########     ########"; i; perms_derange(i, 1); subfac(i)
Next
For i = 10 To 20
Print Using " ###:   ###################"; i; subfac(i)
Next

' empty keyboard buffer
While InKey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End
```
Output:
```permutations derangements for n = 4
1302 3012 1032 2031 2301 3201 3210 2310 1230
count returned = 9 , !4 calculated = 9

count  counted subfactorial
---------------------------
0:        1            1
1:        0            0
2:        1            1
3:        2            2
4:        9            9
5:       44           44
6:      265          265
7:     1854         1854
8:    14833        14833
9:   133496       133496
10:               1334961
11:              14684570
12:             176214841
13:            2290792932
14:           32071101049
15:          481066515734
16:         7697064251745
17:       130850092279664
18:      2355301661033953
19:     44750731559645106
20:    895014631192902121```

## GAP

```# All of this is built-in
Derangements([1 .. 4]);
# [ [ 2, 1, 4, 3 ], [ 2, 3, 4, 1 ], [ 2, 4, 1, 3 ], [ 3, 1, 4, 2 ], [ 3, 4, 1, 2 ], [ 3, 4, 2, 1 ],
#   [ 4, 1, 2, 3 ], [ 4, 3, 1, 2 ], [ 4, 3, 2, 1 ] ]
Size(last);
# 9

NrDerangements([1 .. 4]);
# 9

# An implementation using formula D(n + 1) = n*(D(n) + D(n - 1))
NrDerangementsAlt_memo := [1, 0];
NrDerangementsAlt := function(n)
if not IsBound(NrDerangementsAlt_memo[n + 1]) then
NrDerangementsAlt_memo[n + 1] := (n - 1)*(NrDerangementsAlt(n - 1) + NrDerangementsAlt(n - 2));
fi;
return NrDerangementsAlt_memo[n + 1];
end;

L := List([0 .. 9]);

PrintArray(TransposedMat([L,
List(L, n -> Size(Derangements([1 .. n]))),
List(L, n -> NrDerangements([1 .. n])),
List(L, NrDerangementsAlt)]));
# [ [       0,       1,       1,       1 ],
#   [       1,       0,       0,       0 ],
#   [       2,       1,       1,       1 ],
#   [       3,       2,       2,       2 ],
#   [       4,       9,       9,       9 ],
#   [       5,      44,      44,      44 ],
#   [       6,     265,     265,     265 ],
#   [       7,    1854,    1854,    1854 ],
#   [       8,   14833,   14833,   14833 ],
#   [       9,  133496,  133496,  133496 ] ]
```

## Go

```package main

import (
"fmt"
"math/big"
)

// task 1: function returns list of derangements of n integers
func dList(n int) (r [][]int) {
a := make([]int, n)
for i := range a {
a[i] = i
}
// recursive closure permutes a
var recurse func(last int)
recurse = func(last int) {
if last == 0 {
// bottom of recursion.  you get here once for each permutation.
// test if permutation is deranged.
for j, v := range a {
if j == v {
return // no, ignore it
}
}
// yes, save a copy
r = append(r, append([]int{}, a...))
return
}
for i := last; i >= 0; i-- {
a[i], a[last] = a[last], a[i]
recurse(last - 1)
a[i], a[last] = a[last], a[i]
}
}
recurse(n - 1)
return
}

// task 3: function computes subfactorial of n
func subFact(n int) *big.Int {
if n == 0 {
return big.NewInt(1)
} else if n == 1 {
return big.NewInt(0)
}
d0 := big.NewInt(1)
d1 := big.NewInt(0)
f := new(big.Int)
for i, n64 := int64(1), int64(n); i < n64; i++ {
d0, d1 = d1, d0.Mul(f.SetInt64(i), d0.Add(d0, d1))
}
return d1
}

func main() {
fmt.Println("Derangements of 4 integers")
for _, d := range dList(4) {
fmt.Println(d)
}

fmt.Println("\nNumber of derangements")
fmt.Println("N  Counted  Calculated")
for n := 0; n <= 9; n++ {
fmt.Printf("%d %8d %11s\n", n, len(dList(n)), subFact(n).String())
}

// stretch (sic)
fmt.Println("\n!20 =", subFact(20))
}
```
Output:
```Derangements of 4 integers
[1 0 3 2]
[3 0 1 2]
[1 3 0 2]
[2 0 3 1]
[2 3 0 1]
[3 2 0 1]
[3 2 1 0]
[2 3 1 0]
[1 2 3 0]

Number of derangements
N  Counted  Calculated
0        0           1
1        0           0
2        1           1
3        2           2
4        9           9
5       44          44
6      265         265
7     1854        1854
8    14833       14833
9   133496      133496

!20 = 895014631192902121
```

## Groovy

Solution:

```def fact = { n -> [1,(1..<(n+1)).inject(1) { prod, i -> prod * i }].max() }
def subfact
subfact = { BigInteger n -> (n == 0) ? 1 : (n == 1) ? 0 : ((n-1) * (subfact(n-1) + subfact(n-2))) }

def derangement = { List l ->
def d = []
if (l) l.eachPermutation { p -> if ([p,l].transpose().every{ pp, ll -> pp != ll }) d << p }
d
}
```

Test:

```def d = derangement([1,2,3,4])
assert d.size() == subfact(4)
d.each { println it }

println """
n   # derangements   subfactorial
=   ==============   ============"""
(0..9). each { n ->
def dr = derangement((1..<(n+1)) as List)
def sf = subfact(n)
printf('%1d   %14d   %12d\n', n, dr.size(), sf)
}

println """
!20 == \${subfact(20)}
"""
```
Output:
```[2, 1, 4, 3]
[2, 3, 4, 1]
[2, 4, 1, 3]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 3, 1, 2]
[4, 3, 2, 1]

n   # derangements   subfactorial
=   ==============   ============
0                1              1
1                0              0
2                1              1
3                2              2
4                9              9
5               44             44
6              265            265
7             1854           1854
8            14833          14833
9           133496         133496

!20 == 895014631192902121```

```import Control.Monad (forM_)

import Data.List (permutations)

-- Compute all derangements of a list
derangements
:: Eq a
=> [a] -> [[a]]
derangements = (\x -> filter (and . zipWith (/=) x)) <*> permutations

-- Compute the number of derangements of n elements
subfactorial
:: (Eq a, Num a)
=> a -> a
subfactorial 0 = 1
subfactorial 1 = 0
subfactorial n = (n - 1) * (subfactorial (n - 1) + subfactorial (n - 2))

main :: IO ()
main
-- Generate and show all the derangements of four integers
= do
print \$ derangements [1 .. 4]
putStrLn ""
-- Print the count of derangements vs subfactorial
forM_ [1 .. 9] \$
\i ->
putStrLn \$
mconcat
[show (length (derangements [1 .. i])), " ", show (subfactorial i)]
putStrLn ""
-- Print the number of derangements in a list of 20 items
print \$ subfactorial 20
```
Output:
```[[4,3,2,1],[3,4,2,1],[2,3,4,1],[4,1,2,3],[2,4,1,3],[2,1,4,3],[4,3,1,2],[3,4,1,2],[3,1,4,2]]

0 0
1 1
2 2
9 9
44 44
265 265
1854 1854
14833 14833
133496 133496

895014631192902121```

Alternatively, this is a backtracking method:

```derangements xs = loop xs xs
where loop [] [] = [[]]
loop (h:hs) xs = [x:ys | x <- xs, x /= h, ys <- loop hs (delete x xs)]
```

Since the value i cannot occur in position i, we prefix i on all other derangements from 1 to n that do not include i. The first method of filtering permutations is significantly faster, in practice, however.

## J

Note: `!n` in J denotes factorial (or gamma n+1), and not subfactorial.

```derangement=: (A.&i.~ !)~ (*/ .~: # [) i.  NB. task item 1
subfactorial=: ! * +/@(_1&^ % !)@i.@>:  NB. task item 3
```

Requested examples:

```   derangement 4 NB. task item 2
1 0 3 2
1 2 3 0
1 3 0 2
2 0 3 1
2 3 0 1
2 3 1 0
3 0 1 2
3 2 0 1
3 2 1 0
(,subfactorial,#@derangement)"0 i.10  NB. task item 4
0      1      1
1      0      0
2      1      1
3      2      2
4      9      9
5     44     44
6    265    265
7   1854   1854
8  14833  14833
9 133496 133496
8.95015e17
subfactorial 20x NB. using extended precision
895014631192902121
```

Note that derangement 10 was painfully slow (almost 3 seconds, about 10 times slower than derangement 9 and 100 times slower than derangement 8) -- this is a brute force approach. But brute force seems like an appropriate solution here, since factorial divided by subfactorial asymptotically approaches a value near 0.367879 (the reciprocal of e).

## Java

Translation of: D
```import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Derangement {

public static void main(String[] args) {
System.out.println("derangements for n = 4\n");
for (Object d  : (ArrayList)(derangements(4, false)[0])) {
System.out.println(Arrays.toString((int[])d));
}

System.out.println("\ntable of n vs counted vs calculated derangements\n");
for (int i = 0; i < 10; i++) {
int d = ((Integer)derangements(i, true)[1]).intValue();
System.out.printf("%d  %-7d %-7d\n", i, d, subfact(i));
}

System.out.printf ("\n!20 = %20d\n", subfact(20L));
}

static Object[] derangements(int n, boolean countOnly) {
int[] seq = iota(n);
int[] ori = Arrays.copyOf(seq, n);
long tot = fact(n);

List<int[]> all = new ArrayList<int[]>();
int cnt = n == 0 ? 1 : 0;

while (--tot > 0) {
int j = n - 2;
while (seq[j] > seq[j + 1]) {
j--;
}
int k = n - 1;
while (seq[j] > seq[k]) {
k--;
}
swap(seq, k, j);

int r = n - 1;
int s = j + 1;
while (r > s) {
swap(seq, s, r);
r--;
s++;
}

j = 0;
while (j < n && seq[j] != ori[j]) {
j++;
}
if (j == n) {
if (countOnly) {
cnt++;
} else {
}
}
}
return new Object[]{all, cnt};
}

static long fact(long n) {
long result = 1;
for (long i = 2; i <= n; i++) {
result *= i;
}
return result;
}

static long subfact(long n) {
if (0 <= n && n <= 2) {
return n != 1 ? 1 : 0;
}
return (n - 1) * (subfact(n - 1) + subfact(n - 2));
}

static void swap(int[] arr, int lhs, int rhs) {
int tmp = arr[lhs];
arr[lhs] = arr[rhs];
arr[rhs] = tmp;
}

static int[] iota(int n) {
if (n < 0) {
throw new IllegalArgumentException("iota cannot accept < 0");
}
int[] r = new int[n];
for (int i = 0; i < n; i++) {
r[i] = i;
}
return r;
}
}
```
```derangements for n = 4

[1, 0, 3, 2]
[1, 2, 3, 0]
[1, 3, 0, 2]
[2, 0, 3, 1]
[2, 3, 0, 1]
[2, 3, 1, 0]
[3, 0, 1, 2]
[3, 2, 0, 1]
[3, 2, 1, 0]

table of n vs counted vs calculated derangements

0  1       1
1  0       0
2  1       1
3  2       2
4  9       9
5  44      44
6  265     265
7  1854    1854
8  14833   14833
9  133496  133496

!20 =   895014631192902121```

## jq

Works with: jq version 1.4

The following implementation of "derangements" generates the derangements directly, without generating all permutations. Since recent versions of jq have tail-call optimization (TCO) for arity-0 recursive functions, the workhorse inner function (deranged/0) is implemented as an arity-0 function.

```def derangements:

# In order to reference the original array conveniently, define _derangements(ary):
def _derangements(ary):
# We cannot put the i-th element in the i-th place:
def deranged:  # state: [i, available]
.[0] as \$i | .[1] as \$in
| if \$i == (ary|length) then []
else
(\$in[] | select (. != ary[\$i])) as \$j
|  [\$j] + ([\$i+1, (\$in - [\$j])] | deranged)
end
;
[0,ary]|deranged;
. as \$in | _derangements(\$in);

def subfact:
if . == 0 then 1
elif . == 1 then 0
else (.-1) * (((.-1)|subfact) + ((.-2)|subfact))
end;

# Avoid creating an array just to count the items in a stream:
def count(g): reduce g as \$i (0; . + 1);```

``` "Derangements:",
([range(1;5)] | derangements),
"",
"Counted vs Computed Derangments:",
(range(1;10) as \$i | "\(\$i): \(count( [range(0;\$i)] | derangements)) vs \(\$i|subfact)"),
"",
"Computed approximation to !20 (15 significant digits): \(20|subfact)"```
Output:
```\$ jq -n -c -r -f derangements.jq
jq -n -c -r -f derangements.jq

Derangements:
[2,1,4,3]
[2,3,4,1]
[2,4,1,3]
[3,1,4,2]
[3,4,1,2]
[3,4,2,1]
[4,1,2,3]
[4,3,1,2]
[4,3,2,1]

Counted vs Computed Derangments:
1: 0 vs 0
2: 1 vs 1
3: 2 vs 2
4: 9 vs 9
5: 44 vs 44
6: 265 vs 265
7: 1854 vs 1854
8: 14833 vs 14833
9: 133496 vs 133496

Computed approximation to !20 (15 significant digits): 895014631192902000
```

## Julia

```using Printf, Combinatorics

derangements(n::Int) = (perm for perm in permutations(1:n)
if all(indx != p for (indx, p) in enumerate(perm)))

function subfact(n::Integer)::Integer
if n in (0, 2)
return 1
elseif n == 1
return 0
elseif 1 ≤ n ≤ 18
return round(Int, factorial(n) / e)
elseif n > 0
return (n - 1) * ( subfact(n - 1) + subfact(n - 2) )
else
error()
end
end

println("Derangements of [1, 2, 3, 4]")
for perm in derangements(4)
println(perm)
end

@printf("\n%5s%13s%13s\n", "n", "derangements", "!n")
for n in 1:10
ders = derangements(n)
subf = subfact(n)
@printf("%5i%13i%13i\n", n, length(collect(ders)), subf)
end

println("\n!20 = ", subfact(20))
```
Output:
```Derangements of [1, 2, 3, 4]
[2, 1, 4, 3]
[2, 3, 4, 1]
[2, 4, 1, 3]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 3, 1, 2]
[4, 3, 2, 1]

n derangements           !n
1            0            0
2            1            1
3            2            2
4            9            9
5           44           44
6          265          265
7         1854         1854
8        14833        14833
9       133496       133496
10      1334961      1334961

!20 = 895014631192902121```

## Kotlin

```// version 1.1.2

fun <T> permute(input: List<T>): List<List<T>> {
if (input.size == 1) return listOf(input)
val perms = mutableListOf<List<T>>()
val toInsert = input[0]
for (perm in permute(input.drop(1))) {
for (i in 0..perm.size) {
val newPerm = perm.toMutableList()
}
}
return perms
}

fun derange(input: List<Int>): List<List<Int>> {
if (input.isEmpty()) return listOf(input)
return permute(input).filter { permutation ->
permutation.filterIndexed { i, index -> i == index }.none()
}
}

fun subFactorial(n: Int): Long =
when (n) {
0 -> 1
1 -> 0
else -> (n - 1) * (subFactorial(n - 1) + subFactorial(n - 2))
}

fun main(args: Array<String>) {
val input = listOf(0, 1, 2, 3)

val derangements = derange(input)
println("There are \${derangements.size} derangements of \$input, namely:\n")
derangements.forEach(::println)

println("\nN  Counted   Calculated")
println("-  -------   ----------")
for (n in 0..9) {
val list = List(n) { it }
val counted = derange(list).size
println("%d  %-9d %-9d".format(n, counted, subFactorial(n)))
}
println("\n!20 = \${subFactorial(20)}")
}
```
Output:
```There are 9 derangements of [0, 1, 2, 3], namely:

[1, 2, 3, 0]
[2, 0, 3, 1]
[2, 3, 0, 1]
[2, 3, 1, 0]
[1, 0, 3, 2]
[1, 3, 0, 2]
[3, 0, 1, 2]
[3, 2, 0, 1]
[3, 2, 1, 0]

N  Counted   Calculated
-  -------   ----------
0  1         1
1  0         0
2  1         1
3  2         2
4  9         9
5  44        44
6  265       265
7  1854      1854
8  14833     14833
9  133496    133496

!20 = 895014631192902121
```

## Lua

```-- Return an iterator to produce every permutation of list
function permute (list)
local function perm (list, n)
if n == 0 then coroutine.yield(list) end
for i = 1, n do
list[i], list[n] = list[n], list[i]
perm(list, n - 1)
list[i], list[n] = list[n], list[i]
end
end
return coroutine.wrap(function() perm(list, #list) end)
end

-- Return a copy of table t (wouldn't work for a table of tables)
function copy (t)
if not t then return nil end
local new = {}
for k, v in pairs(t) do new[k] = v end
return new
end

-- Return true if no value in t1 can be found at the same index of t2
function noMatches (t1, t2)
for k, v in pairs(t1) do
if t2[k] == v then return false end
end
return true
end

-- Return a table of all derangements of table t
function derangements (t)
local orig = copy(t)
local nextPerm, deranged = permute(t), {}
local numList, keep = copy(nextPerm())
while numList do
if noMatches(numList, orig) then table.insert(deranged, numList) end
numList = copy(nextPerm())
end
return deranged
end

-- Return the subfactorial of n
function subFact (n)
if n < 2 then
return 1 - n
else
return (subFact(n - 1) + subFact(n - 2)) * (n - 1)
end
end

-- Return a table of the numbers 1 to n
function listOneTo (n)
local t = {}
for i = 1, n do t[i] = i end
return t
end

-- Main procedure
print("Derangements of [1,2,3,4]")
for k, v in pairs(derangements(listOneTo(4))) do print("", unpack(v)) end
print("\n\nSubfactorial vs counted derangements\n")
print("\tn\t| subFact(n)\t| Derangements")
print("    " .. string.rep("-", 42))
for i = 0, 9 do
io.write("\t" .. i .. "\t|  " .. subFact(i))
if string.len(subFact(i)) < 5 then io.write("\t") end
print("\t|  " .. #derangements(listOneTo(i)))
end
print("\n\nThe subfactorial of 20 is " .. subFact(20))
```
Output:
```Derangements of [1,2,3,4]
2       3       4       1
3       4       2       1
4       3       2       1
4       3       1       2
3       4       1       2
3       1       4       2
2       4       1       3
4       1       2       3
2       1       4       3

Subfactorial vs counted derangements

n       | subFact(n)    | Derangements
------------------------------------------
0       |  1            |  1
1       |  0            |  0
2       |  1            |  1
3       |  2            |  2
4       |  9            |  9
5       |  44           |  44
6       |  265          |  265
7       |  1854         |  1854
8       |  14833        |  14833
9       |  133496       |  133496

The subfactorial of 20 is 8.950146311929e+17```

## Mathematica /Wolfram Language

```Needs["Combinatorica`"]
derangements[n_] := Derangements[Range[n]]
derangements[4]
Table[{NumberOfDerangements[i], Subfactorial[i]}, {i, 9}] // TableForm
Subfactorial[20]
```
Output:
```{{2, 1, 4, 3}, {2, 3, 4, 1}, {2, 4, 1, 3}, {3, 1, 4, 2}, {3, 4, 1, 2},
{3, 4, 2, 1}, {4, 1, 2, 3}, {4, 3, 1, 2}, {4, 3, 2, 1}}

0	0
1	1
2	2
9	9
44	44
265	265
1854	1854
14833	14833
133496	133496

895014631192902121```

## Nim

```import algorithm, sequtils, strformat, strutils, tables

iterator derangements[T](a: openArray[T]): seq[T] =
var perm = @a
while true:
if not perm.nextPermutation():
break
block checkDerangement:
for i, val in a:
if perm[i] == val: break checkDerangement
yield perm

proc `!`(n: Natural): Natural =
if n <= 1: return 1 - n
result = (n - 1) * (!(n - 1) + !(n - 2))

echo "Derangements of 1 2 3 4:"
for d in [1, 2, 3, 4].derangements():
echo d.join(" ")

echo "\nNumber of derangements:"
echo "n   counted   calculated"
echo "-   -------   ----------"
for n in 0..9:
echo &"{n}   {toSeq(derangements(toSeq(1..n))).len:>6}      {!n:>6}"

echo "\n!20 = ", !20
```
Output:
```Derangements of 1 2 3 4:
2 1 4 3
2 3 4 1
2 4 1 3
3 1 4 2
3 4 1 2
3 4 2 1
4 1 2 3
4 3 1 2
4 3 2 1

Number of derangements:
n   counted   calculated
-   -------   ----------
0        0           1
1        0           0
2        1           1
3        2           2
4        9           9
5       44          44
6      265         265
7     1854        1854
8    14833       14833
9   133496      133496

!20 = 895014631192902121```

## PARI/GP

```derangements(n)=if(n,round(n!/exp(1)),1);
derange(n)={
my(v=[[]],tmp);
for(level=1,n,
tmp=List();
for(i=1,#v,
for(k=1,n,
if(k==level, next);
for(j=1,level-1,if(v[i][j]==k, next(2)));
listput(tmp, concat(v[i],k))
)
);
v=Vec(tmp)
);
v
};
derange(4)
for(n=0,9,print("!"n" = "#derange(n)" = "derangements(n)))
derangements(20)```
Output:
```%1 = [[2, 1, 4, 3], [2, 3, 4, 1], [2, 4, 1, 3], [3, 1, 4, 2], [3, 4, 1, 2], [3, 4, 2, 1], [4, 1, 2, 3], [4, 3, 1, 2], [4, 3, 2, 1]]

!0 = 1 = 1
!1 = 0 = 0
!2 = 1 = 1
!3 = 2 = 2
!4 = 9 = 9
!5 = 44 = 44
!6 = 265 = 265
!7 = 1854 = 1854
!8 = 14833 = 14833
!9 = 133496 = 133496

%2 = 895014631192902121```

## Pascal

```program Derangements_RC;
(*
Pascal solution for Rosetta Code task "Permutations/Derangements"
Console program written in Free Pascal (Lazarus)
*)
// Returns first derangement in lexicographic order.
// Function return is false if there are no derangements.
function FirstDerangement( var val : array of integer) : boolean;
var
n, j : integer;
begin
n := Length( val);
result := (n <> 1);
if n < 2 then exit;
if Odd(n) then begin
val[n - 3] := n - 2;
val[n - 2] := n - 1;
val[n - 1] := n - 3;
dec( n, 3);
end;
j := 0;
while (j < n) do begin
val[j] := j + 1;
val[j + 1] := j;
inc( j, 2);
end;
end;

// Returns next derangement in lexicographic order.
// Function return is false if there are no more derangements.
// Finds next derangement directly, i.e. not by generating
//   permutations until a derangement is found.
function NextDerangement( var val : array of integer) : boolean;
var
i, j, n : integer;
backward, done : boolean;
free : array of boolean;
begin
n := Length( val);
if (n < 3) then begin
result := false;
exit;
end;
SetLength( free, n);
for j := 0 to n - 1  do free[j] := false;
i := n - 1;
free[val[i]] := true;
backward := true;
done := false;
repeat
if backward then begin
dec(i);  j := val[i];  free[j] := true;
end
else begin
inc(i);  j := -1;
end;
repeat
inc(j)
until (j >= n) or (free[j] and (j <> i));
if (j < n) then begin // found a suitable free value
val[i] := j;  free[j] := false;
if (i = n - 1) then done := true // found the next derangement
else backward := false;
end
else if (i = 0) then done := true // no more derangements
else backward := true;
until done;
result := (i > 0);
end;

// Finds all derangements of integers 0..(n - 1) and
//   returns the number of derangements.
// if boolean "show" is true, writes derangments to standard output.
function FindDerangements( n : integer;
show : boolean) : integer;
var
int_array : array of integer;
j : integer;
ok : boolean;
begin
result := 0;
if (n < 0) then exit;
SetLength( int_array, n);
ok := FirstDerangement( int_array);
while ok do begin
inc( result);
if show then begin
for j := 0 to n - 1 do Write( ' ', int_array[j]);
WriteLn();
end;
ok := NextDerangement( int_array);
end;
end;

// Returns subfactorial of passed-in integer.
function Subfactorial( n : integer) : uint64;
var
j : integer;
begin
result := 1;
for j := 1 to n do begin
result := result*j;
if Odd(j) then dec(result) else inc(result);
end;
end;

// Main routine for Rosetta Code task.
var
n, nrFound, nrCalc : integer;
begin
WriteLn( 'Derangements of 4 integers');
nrFound := FindDerangements( 4, true);
WriteLn( 'Number of derangements found = ', nrFound);
WriteLn();
WriteLn( 'Number of derangements');
WriteLn( '  n   Found    Subfactorial');
for n := 0 to 9 do begin
nrFound := FindDerangements( n, false);
nrCalc  := Subfactorial( n);
WriteLn( n:3, nrFound:8, nrCalc:8);
end;
WriteLn();
WriteLn( 'Subfactorial(20) = ', Subfactorial(20));
end.
```
Output:
```Derangements of 4 integers
1 0 3 2
1 2 3 0
1 3 0 2
2 0 3 1
2 3 0 1
2 3 1 0
3 0 1 2
3 2 0 1
3 2 1 0
Number of derangements found = 9

Number of derangements
n   Found    Subfactorial
0       1       1
1       0       0
2       1       1
3       2       2
4       9       9
5      44      44
6     265     265
7    1854    1854
8   14833   14833
9  133496  133496

Subfactorial(20) = 895014631192902121
```

## Perl

```sub d {
# compare this with the deranged() sub to see how to turn procedural
# code into functional one ('functional' as not in 'understandable')
\$#_ ? map d([ @{\$_[0]}, \$_[\$_] ], @_[1 .. \$_-1, \$_+1 .. \$#_ ]),
grep { \$_[\$_] != @{\$_[0]} } 1 .. \$#_
: \$_[0]
}

sub deranged {  # same as sub d above, just a readable version to explain method
my (\$result, @avail) = @_;
return \$result if !@avail;              # no more elements to pick from, done

my @list;                               # list of permutations to return
for my \$i (0 .. \$#avail) {              # try to add each element to result in turn
next if \$avail[\$i] == @\$result; # element n at n-th position, no-no
my \$e = splice @avail, \$i, 1;   # move the n-th element from available to result
push @list, deranged([ @\$result, \$e ], @avail);
# and recurse down, keep what's returned
splice @avail, \$i, 0, \$e;       # put that element back, try next
}
return @list;
}

sub choose {    # choose k among n, i.e. n! / k! (n-k)!
my (\$n, \$k) = @_;
factorial(\$n) / factorial(\$k) / factorial(\$n - \$k)
}

my @fact = (1);
sub factorial {
# //= : standard caching technique.  If cached value available,
#       return it; else compute, cache and return.
#       For this specific task not really necessary.
\$fact[ \$_[0] ] //= \$_[0] * factorial(\$_[0] - 1)
}

my @subfact;
sub sub_factorial {
my \$n = shift;
\$subfact[\$n] //= do     # same caching stuff, try comment out this line
{
# computes deranged without formula, using recursion
my \$total = factorial(\$n);      # total permutations
for my \$k (1 .. \$n) {
# minus the permutations where k items are fixed
# to original location, and the rest deranged
\$total -= choose(\$n, \$k) * sub_factorial(\$n - \$k)
}
\$total
}
}

print "Derangements for 4 elements:\n";
my @deranged = d([], 0 .. 3);
for (1 .. @deranged) {
print "\$_: @{\$deranged[\$_-1]}\n"
}

print "\nCompare list length and calculated table\n";
for (0 .. 9) {
my @x = d([], 0 .. \$_-1);
print \$_, "\t", scalar(@x), "\t", sub_factorial(\$_), "\n"
}

print "\nNumber of derangements:\n";
print "\$_:\t", sub_factorial(\$_), "\n" for 1 .. 20;
```
Output:
```Derangements for 4 elements:
1: 1 0 3 2
2: 1 2 3 0
3: 1 3 0 2
4: 2 0 3 1
5: 2 3 0 1
6: 2 3 1 0
7: 3 0 1 2
8: 3 2 0 1
9: 3 2 1 0

Compare list length and calculated table
0       1       1
1       0       0
2       1       1
3       2       2
4       9       9
5       44      44
6       265     265
7       1854    1854
8       14833   14833
9       133496  133496

Number of derangements:
1:      0
2:      1
3:      2
4:      9
5:      44
6:      265
7:      1854
8:      14833
9:      133496
10:     1334961
11:     14684570
12:     176214841
13:     2290792932
14:     32071101049
15:     481066515734
16:     7697064251745
17:     130850092279664
18:     2355301661033953
19:     44750731559645106
20:     895014631192902121```

### Using a module

Library: ntheory
```use ntheory ":all";

# Count derangements using derangement iterator
sub countderange {
my(\$n,\$s) = (shift,0);
forderange { \$s++ } \$n;
\$s;
}
# Count derangements using inclusion-exclusion
sub subfactorial1 {
my \$n = shift;
vecsum(map{ vecprod((-1)**(\$n-\$_),binomial(\$n,\$_),factorial(\$_)) }0..\$n);
}
# Count derangements using simple recursion without special functions
sub subfactorial2 {
my \$n = shift;
use bigint;  no warnings 'recursion';
(\$n < 1)  ?  1  :  \$n * subfactorial2(\$n-1) + (-1)**\$n;
}

print "Derangements of 4 items:\n";
forderange { print "@_\n" } 4;
printf "\n%3s %15s %15s\n","N","List count","!N";
printf "%3d %15d %15d %15d\n",\$_,countderange(\$_),subfactorial1(\$_),subfactorial2(\$_) for 0..9;
printf "%3d %15s %s\n",\$_,"",subfactorial2(\$_) for 20,200;
```
Output:
```Derangements of 4 items:
1 0 3 2
1 2 3 0
1 3 0 2
2 0 3 1
2 3 0 1
2 3 1 0
3 0 1 2
3 2 0 1
3 2 1 0

N      List count   !N (binomial)  !N (recursion)
0               1               1               1
1               0               0               0
2               1               1               1
3               2               2               2
4               9               9               9
5              44              44              44
6             265             265             265
7            1854            1854            1854
8           14833           14833           14833
9          133496          133496          133496
20                 895014631192902121
200                 290131015521620609254546237518688936375622413566095185632876940298382875066633305125595907908697818551860745708196640009079772455670451355426573609799907339222509103785567575227183775791345718826220455840965346196540544976439608810006794385963854831693077054723298130736781093200499800934036993104223443563872463385599425635345341317933466521378117877578807421014599223577201
```

## Phix

Library: Phix/mpfr
```with javascript_semantics
function deranged(sequence s1, sequence s2)
for i=1 to length(s1) do
if s1[i]==s2[i] then return 0 end if
end for
return 1
end function

function derangements(integer n)
sequence ts = tagset(n)
sequence res = {}
for i=1 to factorial(n) do
sequence s = permute(i,ts)
if deranged(s,ts) then
res = append(res,s)
end if
end for
return res
end function

function subfactorial(integer n)
if n<2 then return 1-n end if
return (n-1)*(subfactorial(n-1)+subfactorial(n-2))
end function

?derangements(4)
for n=0 to 9 do
printf(1,"%d: counted:%d, calculated:%d\n",{n,length(derangements(n)),subfactorial(n)})
end for
string msg = iff(machine_bits()=32?" (incorrect on 32-bit!)":"") -- (fine on 64-bit)
printf(1,"!20=%d%s\n",{subfactorial(20),msg})

include mpfr.e
function mpz_sub_factorial(integer n)
-- probably not the most efficient way to do this!
if n<2 then return sprintf("%d",{1-n}) end if
mpz f = mpz_init(mpz_sub_factorial(n-1)),
g = mpz_init(mpz_sub_factorial(n-2))
mpz_mul_si(f,f,n-1)
string res = mpz_get_str(f)
{f,g} = mpz_free({f,g})
return res
end function
printf(1,"!20=%s (mpfr)\n",{mpz_sub_factorial(20)})
```
Output:
```{{2,3,4,1},{4,3,1,2},{2,4,1,3},{3,4,2,1},{3,1,4,2},{4,1,2,3},{2,1,4,3},{3,4,1,2},{4,3,2,1}}
0: counted:1, calculated:1
1: counted:0, calculated:0
2: counted:1, calculated:1
3: counted:2, calculated:2
4: counted:9, calculated:9
5: counted:44, calculated:44
6: counted:265, calculated:265
7: counted:1854, calculated:1854
8: counted:14833, calculated:14833
9: counted:133496, calculated:133496
!20=895014631192902186 (incorrect on 32-bit!)
!20=895014631192902121 (mpfr)
```

(under pwa/p2js you get a trailing "000" instead of "186" for the incorrect result)

Translation of: FreeBASIC

A more efficient method of calculating subfactorials (0 should be handled separately, or obviously prepend a 1 and extract with idx+1).
Should you instead of string results want an array of mpz for further calculations, use the mpz_init_set() call as shown:

```with javascript_semantics
include mpfr.e

function subfactorial(integer n)
sequence res = repeat(0,n)
mpz num = mpz_init(1)

for i=1 to n do
mpz_mul_si(num,num,i)
if mpz_odd(num) then
mpz_sub_ui(num,num,1)
else
end if
res[i] = mpz_get_str(num)
--      res[i] = mpz_init_set(num)
end for
return res
end function

?extract(subfactorial(20),tagset(9)&20)
```
Output:
`{"0","1","2","9","44","265","1854","14833","133496","895014631192902121"}`

## Picat

```import util.

go =>
foreach(N in 0..9)
println([N,num_derangements=num_derangements(N), subfactorial=subfactorial(N), subfactorial2=subfactorial2(N)])
end,
println(["!20", subfactorial(20)]),
println(["!20 approx", subfactorial2(20)]),
println("subfactorial0..30"=[subfactorial(N) : N in 0..30 ]),
println("subfactorial2_0..30"=[subfactorial2(N) : N in 0..30 ]),
println(["!200", subfactorial(200)]),
nl,
println("Syntax sugar:"),
println("'!'(20)"='!'(20)),
println("200.'!'()"=200.'!'()),
println("'!!'(20)"='!!'(20)),
println("'!-!!'(10)"='!-!!'(10)),
nl.

num_derangements(N) = derangements(N).length.

derangements(N) = D =>
D = [P : P in permutations(1..N), nofixpoint(P)].

% subfactorial: tabled recursive function
table
subfactorial(0) = 1.
subfactorial(1) = 0.
subfactorial(N) = (N-1)*(subfactorial(N-1)+subfactorial(N-2)).

% approximate version of subfactorial
subfactorial2(0) = 1.
subfactorial2(N) = floor(1.0*floor(factorial(N)/2.71828 + 1/2.0)).

% Factorial
fact(N) = F =>
F1 = 1,
foreach(I in 1..N)
F1 := F1 * I
end,
F = F1.

% No fixpoint in L
nofixpoint(L) =>
foreach(I in 1..L.length)
L[I] != I
end.

% Some syntax sugar. Note: the function must be an atom.
'!'(N) = fact(N).
'!!'(N) = subfactorial(N).

'!-!!'(N) = fact(N) - subfactorial(N).```
Output:
```[0,num_derangements = 1,subfactorial = 1,subfactorial2 = 1]
[1,num_derangements = 0,subfactorial = 0,subfactorial2 = 0]
[2,num_derangements = 1,subfactorial = 1,subfactorial2 = 1]
[3,num_derangements = 2,subfactorial = 2,subfactorial2 = 2]
[4,num_derangements = 9,subfactorial = 9,subfactorial2 = 9]
[5,num_derangements = 44,subfactorial = 44,subfactorial2 = 44]
[6,num_derangements = 265,subfactorial = 265,subfactorial2 = 265]
[7,num_derangements = 1854,subfactorial = 1854,subfactorial2 = 1854]
[8,num_derangements = 14833,subfactorial = 14833,subfactorial2 = 14833]
[9,num_derangements = 133496,subfactorial = 133496,subfactorial2 = 133496]
[!20,895014631192902121]
[!20 approx,895015233227128960]
subfactorial0..30 = [1,0,1,2,9,44,265,1854,14833,133496,1334961,14684570,176214841,2290792932,32071101049,481066515734,7697064251745,130850092279664,2355301661033953,44750731559645106,895014631192902121,18795307255050944540,413496759611120779881,9510425471055777937262,228250211305338670494289,5706255282633466762357224,148362637348470135821287825,4005791208408693667174771274,112162153835443422680893595673,3252702461227859257745914274516,97581073836835777732377428235481]
subfactorial2_0..30 = [1,0,1,2,9,44,265,1854,14833,133496,1334962,14684580,176214959,2290794473,32071122622,481066839325,7697069429198,130850180296364,2355303245334550,44750761661356448,895015233227128960,18795319897769705472,413497037750933585920,9510431868271472934912,228250364838515316883456,5706259120962883593175040,148362737145034969127583744,4005793902915943736948031488,112162229281646435629661159424,3252704649167746668444545712128,97581139475032389920237209780224]
[!200,290131015521620609254546237518688936375622413566095185632876940298382875066633305125595907908697818551860745708196640009079772455670451355426573609799907339222509103785567575227183775791345718826220455840965346196540544976439608810006794385963854831693077054723298130736781093200499800934036993104223443563872463385599425635345341317933466521378117877578807421014599223577201]

Syntax sugar:
'!'(20) = 2432902008176640000
200.'!'() = 788657867364790503552363213932185062295135977687173263294742533244359449963403342920304284011984623904177212138919638830257642790242637105061926624952829931113462857270763317237396988943922445621451664240254033291864131227428294853277524242407573903240321257405579568660226031904170324062351700858796178922222789623703897374720000000000000000000000000000000000000000000000000
'!!'(20) = 895014631192902121
'!-!!'(10) = 2293839```

## PicoLisp

```(load "@lib/simul.l")  # For 'permute'

(de derangements (Lst)
(filter
'((L) (not (find = L Lst)))
(permute Lst) ) )

(de subfact (N)
(if (>= 2 N)
(if (= 1 N) 0 1)
(*
(dec N)
(+ (subfact (dec N)) (subfact (- N 2))) ) ) )```
Output:
```: (derangements (range 1 4))
-> ((2 1 4 3) (2 3 4 1) (2 4 1 3) (3 1 4 2) (3 4 1 2) (3 4 2 1) (4 1 2 3) (4 3 1 2) (4 3 2 1))

: (for I (range 0 9)
(tab (2 8 8)
I
(length (derangements (range 1 I)))
(subfact I) ) )
0       1       1
1       0       0
2       1       1
3       2       2
4       9       9
5      44      44
6     265     265
7    1854    1854
8   14833   14833
9  133496  133496
-> NIL

: (subfact 20)
-> 895014631192902121```

## PureBasic

Brute Force

```Procedure.q Subfactoral(n)
If n=0:ProcedureReturn 1:EndIf
If n=1:ProcedureReturn 0:EndIf
ProcedureReturn (Subfactoral(n-1)+Subfactoral(n-2))*(n-1)
EndProcedure

factFile.s="factorials.txt"
tempFile.s="temp.txt"
drngFile.s="derangements.txt"
DeleteFile(factFile.s)
DeleteFile(tempFile.s)
DeleteFile(drngFile.s)

n=4

; create our storage file
f.s=factFile.s
If CreateFile(0,f.s)
WriteStringN(0,"1.2")
WriteStringN(0,"2.1")
CloseFile(0)
Else
Debug "not createfile :"+f.s
EndIf

showfactorial=#False

If showfactorial
; cw("nfactorial n ="+str(n))
Debug "nfactorial n ="+Str(n)
EndIf

; build up the factorial combinations
For l=1 To n-2
Gosub nfactorial
Next

; extract the derangements
; cw("derangements["+str(perm(n))+"] for n="+str(n))
Debug "derangements["+Str(Subfactoral(n))+"] for n="+Str(n)
Gosub derangements
; cw("")
Debug ""

; show the first 20 derangements
For i=0 To 20
Debug "derangements["+Str(Subfactoral(i))+"] for n="+Str(i)
Next

End

derangements:
x=0
Repeat
cs=CountString(r.s,".")
If cs
hit=0
t.s=""
; scan for numbers at their index
For i=1 To cs+1
s.s=StringField(r.s,i,".")
t.s+s.s+"."
If Val(s.s)=i:hit+1:EndIf
Next
t.s=RTrim(t.s,".")
; show only those which are valid
If Not hit
x+1
; cw(t.s+" "+str(x))
Debug t.s+" "+Str(x)
WriteStringN(1,t.s+" "+Str(x))
EndIf
EndIf
Until Eof(0)
CloseFile(0)
CloseFile(1)
Else
Debug "not createfile :"+drngFile.s
EndIf
; cw("")
Debug ""
Return

nfactorial:
x=0
Repeat
cs=CountString(r.s,".")
If cs
For j=1 To cs+2
t.s=""
For i=1 To cs+1
s.s=StringField(r.s,i,".")
If i=j
t.s+"."+Str(cs+2)+"."+s.s
Else
t.s+"."+s.s
EndIf
Next
If j=cs+2:t.s+"."+Str(cs+2):EndIf
t.s=Trim(t.s,".")
x+1
If cs+2=n And showfactorial
; cw(t.s+" "+str(x))
Debug t.s+" "+Str(x)
EndIf
WriteStringN(1,t.s)
Next
EndIf
Until Eof(0)
CloseFile(0)
CloseFile(1)
Else
Debug "not createfile :"+tempFile.s
EndIf
CopyFile(tempFile.s,factFile.s)
DeleteFile(tempFile.s)
Return
```
Output:
```derangements[9] for n=4
4.3.1.2 1
3.4.1.2 2
3.1.4.2 3
4.1.2.3 4
4.3.2.1 5
3.4.2.1 6
2.3.4.1 7
2.4.1.3 8
2.1.4.3 9

derangements[1] for n=0
derangements[0] for n=1
derangements[1] for n=2
derangements[2] for n=3
derangements[9] for n=4
derangements[44] for n=5
derangements[265] for n=6
derangements[1854] for n=7
derangements[14833] for n=8
derangements[133496] for n=9
derangements[1334961] for n=10
derangements[14684570] for n=11
derangements[176214841] for n=12
derangements[2290792932] for n=13
derangements[32071101049] for n=14
derangements[481066515734] for n=15
derangements[7697064251745] for n=16
derangements[130850092279664] for n=17
derangements[2355301661033953] for n=18
derangements[44750731559645106] for n=19
derangements[895014631192902121] for n=20
```
Translation of: C
```Procedure.i deranged(depth, lenn, Array d(1), show)
Protected count, tmp, i
If depth = lenn
If show
For i = 0 To lenn - 1: Print(Chr(d(i) + 'a')): Next
PrintN("")
EndIf
ProcedureReturn  1
EndIf

For i = lenn - 1 To depth Step -1
If i = d(depth): Continue: EndIf

tmp = d(i): d(i) = d(depth): d(depth) = tmp
count + deranged(depth + 1, lenn, d(), show)
tmp = d(i): d(i) = d(depth): d(depth) = tmp
Next

ProcedureReturn count
EndProcedure

Procedure.q sub_fact(n)
If n = 0: ProcedureReturn 1: EndIf
If n = 1: ProcedureReturn 0: EndIf
ProcedureReturn (sub_fact(n - 1) + sub_fact(n - 2)) * (n - 1)
EndProcedure

Procedure.i gen_n(n, show)
Protected r.i
Dim a(1024)
For i = 0 To n - 1: a(i) = i: Next
ProcedureReturn  deranged(0, n, a(), show)
EndProcedure

If OpenConsole()
PrintN("Deranged Four:")
gen_n(4, 1)

PrintN(#CRLF\$ + "Compare list vs calc:")
For i = 0 To 9
PrintN(Str(i) + ":" + #TAB\$ + Str(gen_n(i, 0)) + #TAB\$ + Str(sub_fact(i)))
Next

PrintN(#CRLF\$ + "further calc:")
For i = 10 To 20
PrintN(Str(i) + ": " + Str(sub_fact(i)))
Next

Print(#CRLF\$ + #CRLF\$ + "Press ENTER to exit"): Input()
CloseConsole()
EndIf
```
Output:
```Deranged Four:
dabc
dcab
dcba
cdba
cdab
bdac
bcda

Compare list vs calc:
0:      1       1
1:      0       0
2:      1       1
3:      2       2
4:      9       9
5:      44      44
6:      265     265
7:      1854    1854
8:      14833   14833
9:      133496  133496

further calc:
10: 1334961
11: 14684570
12: 176214841
13: 2290792932
14: 32071101049
15: 481066515734
16: 7697064251745
17: 130850092279664
18: 2355301661033953
19: 44750731559645106
20: 895014631192902121```

## Python

Includes stretch goal.

```from itertools import permutations
import math

def derangements(n):
'All deranged permutations of the integers 0..n-1 inclusive'
return ( perm for perm in permutations(range(n))
if all(indx != p for indx, p in enumerate(perm)) )

def subfact(n):
if n == 2 or n == 0:
return 1
elif n == 1:
return 0
elif  1 <= n <=18:
return round(math.factorial(n) / math.e)
elif n.imag == 0 and n.real == int(n.real) and n > 0:
return (n-1) * ( subfact(n - 1) + subfact(n - 2) )
else:
raise ValueError()

def _iterlen(iter):
'length of an iterator without taking much memory'
l = 0
for x in iter:
l += 1
return l

if __name__ == '__main__':
n = 4
print("Derangements of %s" % (tuple(range(n)),))
for d in derangements(n):
print("  %s" % (d,))

print("\nTable of n vs counted vs calculated derangements")
for n in range(10):
print("%2i %-5i %-5i" %
(n, _iterlen(derangements(n)), subfact(n)))

n = 20
print("\n!%i = %i" % (n, subfact(n)))
```
Output:
```Derangements of (0, 1, 2, 3)
(1, 0, 3, 2)
(1, 2, 3, 0)
(1, 3, 0, 2)
(2, 0, 3, 1)
(2, 3, 0, 1)
(2, 3, 1, 0)
(3, 0, 1, 2)
(3, 2, 0, 1)
(3, 2, 1, 0)

Table of n vs counted vs calculated derangements
0 1     1
1 0     0
2 1     1
3 2     2
4 9     9
5 44    44
6 265   265
7 1854  1854
8 14833 14833
9 133496 133496

!20 = 895014631192902121```

## QBasic

Works with: QBasic version 1.1
Translation of: FreeBASIC

Error "Subscript out of scope" for n > 7

```' Heap's algorithm non-recursive
FUNCTION permsderange (n!, flag!)
IF n = 0 THEN permsderange = 1

DIM a!(0 TO n), c!(0 TO n)

FOR j = 0 TO n - 1: a(j) = j: NEXT j

WHILE i < n
IF c(i) < i THEN
IF (i AND 1) = 0 THEN
SWAP a(0), a(i)
ELSE
SWAP a(c(i)), a(i)
END IF
FOR j = 0 TO n - 1
IF a(j) = j THEN j = 99
NEXT j
IF j < 99 THEN
count = count + 1
IF flag = 0 THEN
c1 = c1 + 1
FOR j = 0 TO n - 1
PRINT a(j);
NEXT j
IF c1 > 12 THEN
PRINT : c1 = 0
ELSE
PRINT
END IF
END IF
END IF
c(i) = c(i) + 1
i = 0
ELSE
c(i) = 0
i = i + 1
END IF
WEND
IF flag = 0 AND c1 <> 0 THEN PRINT
permsderange = count
END FUNCTION

SUB Subfactorial (a!())
FOR i = 0 TO UBOUND(a)
num = num * i
IF (i AND 1) = 1 THEN
num = num - 1
ELSE
num = num + 1
END IF
a(i) = num
NEXT i
END SUB

n! = 4
DIM subfac!(7)

CALL Subfactorial(subfac())

PRINT "permutations derangements for n = "; n
i! = permsderange(n, 0)
PRINT "count returned ="; i; " , !"; n; " calculated ="; subfac(n)

PRINT
PRINT "count  counted subfactorial"
PRINT "---------------------------"
FOR i = 0 TO 7
PRINT USING " ###: ########     ########"; i; permsderange(i, 1); subfac(i)
NEXT i
```

## Quackery

```  [ stack ]                            is deranges.num (     --> [ )

forward is (deranges)
[ over size
deranges.num share = iff
[ over temp take
swap nested join
temp put ]
else
[ dup size times
[ 2dup i^ pluck
dip [ over size ]
tuck != iff
[ rot swap
nested join
swap (deranges) ]
else
[ drop 2drop ] ] ]
2drop ]                      resolves (deranges)   ( [ [ -->   )

[ dup deranges.num put
[] swap times [ i^ join ]
[] temp put
[] swap (deranges)
temp take
deranges.num release ]             is derangements (   n --> [ )

[ dup 0 = iff [ drop 1 ] done
1 0 rot
1 - times
[ swap over + i^ 1+ * ]
nip ]                              is sub!         (   n --> n )

4 derangements witheach [ echo cr ]
cr
10 times
[ i^ echo sp
i^ derangements size echo sp
i^ sub! echo cr ]
cr
20 sub! echo```
Output:
```[ 1 0 3 2 ]
[ 1 2 3 0 ]
[ 1 3 0 2 ]
[ 2 0 3 1 ]
[ 2 3 0 1 ]
[ 2 3 1 0 ]
[ 3 0 1 2 ]
[ 3 2 0 1 ]
[ 3 2 1 0 ]

0 1 1
1 0 0
2 1 1
3 2 2
4 9 9
5 44 44
6 265 265
7 1854 1854
8 14833 14833
9 133496 133496

895014631192902121```

## Racket

```#lang racket

(define (all-misplaced? l)
(for/and ([x (in-list l)] [n (in-naturals 1)]) (not (= x n))))

;; 1. Create a named function to generate derangements of the integers 0..n-1.
(define (derangements n)
(define (all-misplaced? l1 l2)
(or (null? l1)
(and (not (eq? (car l1) (car l2)))
(all-misplaced? (cdr l1) (cdr l2)))))
(define l (range n))
(for/list ([p (permutations l)] #:when (all-misplaced? p l))
p))

;; 2. Generate and show all the derangements of 4 integers using the above
;;    routine.
(derangements 4)
;; -> '((1 0 3 2) (3 0 1 2) (1 3 0 2) (2 0 3 1) (2 3 0 1)
;;      (3 2 0 1) (1 2 3 0) (2 3 1 0) (3 2 1 0))

;; 3. Create a function that calculates the subfactorial of n, !n.
(define (sub-fact n)
(if (< n 2) (- 1 n)
(* (+ (sub-fact (- n 1)) (sub-fact (- n 2))) (sub1 n))))

;; 4. Print and show a table of the counted number of derangements of n vs. the
;;    calculated !n for n from 0..9 inclusive.
(for ([i 10])
(printf "~a ~a ~a\n" i
(~a #:width 7 #:align 'right (length (derangements i)))
(sub-fact i)))
;; Output:
;; 0       1 1
;; 1       0 0
;; 2       1 1
;; 3       2 2
;; 4       9 9
;; 5      44 44
;; 6     265 265
;; 7    1854 1854
;; 8   14833 14833
;; 9  133496 133496

;; Extra: !20
(sub-fact 20)
;; -> 895014631192902121
```

## Raku

(formerly Perl 6)

Translation of: Perl
Works with: Rakudo version 2016.10

Generate `List.permutations` and keep the ones where no elements are in their original position. This is done by zipping each permutation with the original list, and keeping the ones where none of the zipped pairs are equal.

I am using the `Z` infix zip operator with the `eqv` equivalence infix operator, all wrapped inside a `none()` Junction.

Although not necessary for this task, I have used `eqv` instead of `==` so that the `derangements()` function also works with any set of arbitrary objects (eg. strings, lists, etc.)

```sub derangements(@l) {
@l.permutations.grep(-> @p { none(@p Zeqv @l) })
}

sub prefix:<!>(Int \$n) {
(1, 0, 1, -> \$a, \$b { (\$++ + 2) × (\$b + \$a) } ... *)[\$n]
}

say 'derangements([1, 2, 3, 4])';
say derangements([1, 2, 3, 4]), "\n";

say 'n == !n == derangements(^n).elems';
for 0 .. 9 -> \$n {
say "!\$n == { !\$n } == { derangements(^\$n).elems }"
}
```
Output:
```derangements([1, 2, 3, 4])
((2 1 4 3) (2 3 4 1) (2 4 1 3) (3 1 4 2) (3 4 1 2) (3 4 2 1) (4 1 2 3) (4 3 1 2) (4 3 2 1))

n == !n == derangements(^n).elems
!0 == 1 == 1
!1 == 0 == 0
!2 == 1 == 1
!3 == 2 == 2
!4 == 9 == 9
!5 == 44 == 44
!6 == 265 == 265
!7 == 1854 == 1854
!8 == 14833 == 14833
!9 == 133496 == 133496
```

Much faster to just calculate the subfactorial.

```my @subfactorial = 1,0,{++\$ × (\$^a + \$^b)}…*;

say "!\$_: ",@subfactorial[\$_] for |^10, 20, 200;
```
Output:
```!0: 1
!1: 0
!2: 1
!3: 2
!4: 9
!5: 44
!6: 265
!7: 1854
!8: 14833
!9: 133496
!20: 895014631192902121
!200: 290131015521620609254546237518688936375622413566095185632876940298382875066633305125595907908697818551860745708196640009079772455670451355426573609799907339222509103785567575227183775791345718826220455840965346196540544976439608810006794385963854831693077054723298130736781093200499800934036993104223443563872463385599425635345341317933466521378117877578807421014599223577201```

## REXX

```/*REXX program generates all  permutations  of   N   derangements  and  subfactorial #  */
numeric digits 1000                              /*be able to handle large subfactorials*/
parse arg N .;     if N=='' | N==","  then N=4   /*Not specified?  Then use the default.*/
d= derangeSet(N)                                 /*go and build the  derangements  set. */
say d  'derangements for'    N    "items are:"
say
do i=1  for  d                             /*display the derangements for N items.*/
say right('derangement', 22)       right(i, length(d) )        '───►'         \$.i
end   /*i*/
say                                              /* [↓]  count and calculate subfact !L.*/
do L=0  to 2;  d= derangeSet(L)
say L 'items:  derangement count='right(d, 6)",  !"L'='right( !s(L), 6)
end   /*L*/
say
say right('!20=' , 22)     !s( 20)
say right('!200=', 22)     !s(200)
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
!s:         _=1;      do j=1  for arg(1);  if j//2  then _= j*_  -  1;     else _=j*_  + 1
end   /*j*/;                       return _
/*──────────────────────────────────────────────────────────────────────────────────────*/
derangeSet: procedure expose \$.;  parse arg x;   \$.=;    #=0;   p=x-1
if x==0  then return 1;  if x==1  then return 0
@.1=2;  @.2=1                                    /*populate 1st derangement.*/
do i=3  to x;  @.i=i;  end  /*i*/              /*    "    the rest of 'em.*/
parse value  @.p  @.x   with   @.x  @.p;   call .buildD x    /*swap & build.*/
/*build others.*/
do while .nextD(x, 0);  call .buildD x;   end;                  return #
/*──────────────────────────────────────────────────────────────────────────────────────*/
.buildD:              do j=1  for arg(1);   if @.j==j  then return;  end
#=#+1;    do j=1  for arg(1);   \$.#= \$.# @.j;            end;     return
/*──────────────────────────────────────────────────────────────────────────────────────*/
.nextD:     procedure expose @.;  parse arg n,i

do k=n-1  by -1  for n-1;  kp=k+1;     if @.k<@.kp  then do; i=k; leave; end
end   /*k*/

do j=i+1  while j<n;       parse value  @.j  @.n   with   @.n  @.j;   n=n-1
end   /*j*/
if i==0  then return 0
do m=i+1  while @.m<@.i;   end  /*m*/          /* [↓]  swap two values.   */
parse  value   @.m @.i   with   @.i @.m;                          return 1
```
output   when using the default inputs:
```9 derangements for 4 items are:

derangement 1 ───►  2 1 4 3
derangement 2 ───►  2 3 4 1
derangement 3 ───►  2 4 1 3
derangement 4 ───►  3 1 4 2
derangement 5 ───►  3 4 1 2
derangement 6 ───►  3 4 2 1
derangement 7 ───►  4 1 2 3
derangement 8 ───►  4 3 1 2
derangement 9 ───►  4 3 2 1

0 items:  derangement count=     1,  !0=     1
1 items:  derangement count=     0,  !1=     0
2 items:  derangement count=     1,  !2=     1

!20= 895014631192902121
!200= 290131015521620609254546237518688936375622413566095185632876940298382875066633305125595907908697818551860745708196640009079772455670451355426573609799907339222509103785567575227183775791345718826220455840965346196540544976439608810006794385963854831693077054723298130736781093200499800934036993104223443563872463385599425635345341317933466521378117877578807421014599223577201
```

## Ruby

```def derangements(n)
ary = (1 .. n).to_a
ary.permutation.select do |perm|
ary.zip(perm).all? {|a,b| a != b}
end
end

def subfact(n)
case n
when 0 then 1
when 1 then 0
else (n-1)*(subfact(n-1) + subfact(n-2))
end
end

puts "derangements for n = 4"
derangements(4).each{|d|p d}

puts "\n n   derange  subfact"
(0..9).each do |n|
puts "%2d :%8d,%8d" % [n, derangements(n).size, subfact(n)]
end

puts "\nNumber of derangements"
(10..20).each do |n|
puts "#{n} : #{subfact(n)}"
end
```
Output:
```derangements for n = 4
[2, 1, 4, 3]
[2, 3, 4, 1]
[2, 4, 1, 3]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[4, 1, 2, 3]
[4, 3, 1, 2]
[4, 3, 2, 1]

n   derange  subfact
0 :       1,       1
1 :       0,       0
2 :       1,       1
3 :       2,       2
4 :       9,       9
5 :      44,      44
6 :     265,     265
7 :    1854,    1854
8 :   14833,   14833
9 :  133496,  133496

Number of derangements
10 : 1334961
11 : 14684570
12 : 176214841
13 : 2290792932
14 : 32071101049
15 : 481066515734
16 : 7697064251745
17 : 130850092279664
18 : 2355301661033953
19 : 44750731559645106
20 : 895014631192902121
```

## Scala

Translation of: Ruby
```def derangements(n: Int) =
(1 to n).permutations.filter(_.zipWithIndex.forall{case (a, b) => a - b != 1})

def subfactorial(n: Long): Long = n match {
case 0 => 1
case 1 => 0
case _ => (n - 1) * (subfactorial(n - 1) + subfactorial(n - 2))
}

println(s"Derangements for n = 4")
println(derangements(4) mkString "\n")

println("\n%2s%10s%10s".format("n", "derange", "subfact"))
(0 to 9).foreach(n => println("%2d%10d%10d".format(n, derangements(n).size, subfactorial(n))))
(10 to 20).foreach(n => println(f"\$n%2d\${subfactorial(n)}%20d"))
```
Output:
```Derangements for n = 4
Vector(2, 1, 4, 3)
Vector(2, 3, 4, 1)
Vector(2, 4, 1, 3)
Vector(3, 1, 4, 2)
Vector(3, 4, 1, 2)
Vector(3, 4, 2, 1)
Vector(4, 1, 2, 3)
Vector(4, 3, 1, 2)
Vector(4, 3, 2, 1)

n   derange   subfact
0         1         1
1         0         0
2         1         1
3         2         2
4         9         9
5        44        44
6       265       265
7      1854      1854
8     14833     14833
9    133496    133496
10             1334961
11            14684570
12           176214841
13          2290792932
14         32071101049
15        481066515734
16       7697064251745
17     130850092279664
18    2355301661033953
19   44750731559645106
20  895014631192902121```

## SuperCollider

```(
d = { |array, n|
Routine {
n = n ?? { array.size.factorial };
n.do { |i|
var permuted = array.permute(i);
if(array.every { |each, i| permuted[i] != each }) {
permuted.yield
};
}
};
};
f = { |n| d.((0..n-1)) };
x = f.(4);
x.all.do(_.postln); "";
)
```

```[ 3, 2, 1, 0 ]
[ 2, 3, 0, 1 ]
[ 1, 0, 3, 2 ]
[ 1, 2, 3, 0 ]
[ 2, 0, 3, 1 ]
[ 3, 2, 0, 1 ]
[ 1, 3, 0, 2 ]
[ 2, 3, 1, 0 ]
[ 3, 0, 1, 2 ]
```
```(
z = { |n|
case
{ n <= 0 } { 1 }
{ n == 1 } { 0 }
{ (n - 1) * (z.(n - 1) + z.(n - 2)) }
};
p = { |i| i.asPaddedString(10, " ") };
"n    derangements    subfactorial".postln;
(0..9).do { |i|
var derangements = f.(i).all;
var subfactorial = z.(i);
"%    %    %\n".postf(i, p.(derangements.size), p.(subfactorial));
};
)
```

```n    derangements    subfactorial
0             1             1
1             0             0
2             1             1
3             2             2
4             9             9
5            44            44
6           265           265
7          1854          1854
8         14833         14833
9        133496        133496
```

## Tcl

Library: Tcllib (Package: struct::list)
```package require Tcl 8.5;		# for arbitrary-precision integers
package require struct::list;		# for permutation enumerator

proc derangements lst {
# Special case
if {![llength \$lst]} {return {{}}}
set result {}
for {set perm [struct::list firstperm \$lst]} {[llength \$perm]} \
{set perm [struct::list nextperm \$perm]} {
set skip 0
foreach a \$lst b \$perm {
if {[set skip [string equal \$a \$b]]} break
}
if {!\$skip} {lappend result \$perm}
}
return \$result
}

proc deranged1to n {
for {set i 1;set r {}} {\$i <= \$n} {incr i} {lappend r \$i}
return [derangements \$r]
}

proc countDeranged1to n {
llength [deranged1to \$n]
}

proc subfact n {
if {\$n == 0} {return 1}
if {\$n == 1} {return 0}
set o 1
set s 0
for {set i 1} {\$i < \$n} {incr i} {
set s [expr {\$i * (\$o + [set o \$s])}]
}
return \$s
}
```

Demonstrating with the display parts of the task:

```foreach d [deranged1to 4] {
puts "derangement of 1..4: \$d"
}

puts "\n\tcounted\tcalculated"
for {set i 0} {\$i <= 9} {incr i} {
puts "!\$i\t[countDeranged1to \$i]\t[subfact \$i]"
}

# Stretch goal
puts "\n!20 = [subfact 20]"
```
Output:
```derangement of 1..4: 2 1 4 3
derangement of 1..4: 2 3 4 1
derangement of 1..4: 2 4 1 3
derangement of 1..4: 3 1 4 2
derangement of 1..4: 3 4 1 2
derangement of 1..4: 3 4 2 1
derangement of 1..4: 4 1 2 3
derangement of 1..4: 4 3 1 2
derangement of 1..4: 4 3 2 1

counted	calculated
!0	1	1
!1	0	0
!2	1	1
!3	2	2
!4	9	9
!5	44	44
!6	265	265
!7	1854	1854
!8	14833	14833
!9	133496	133496

!20 = 895014631192902121
```

## Wren

Translation of: Kotlin
Library: Wren-fmt
Library: Wren-big
```import "./fmt" for Fmt
import "./big" for BigInt

var permute // recursive
permute = Fn.new { |input|
if (input.count == 1) return [input]
var perms = []
var toInsert = input[0]
for (perm in permute.call(input[1..-1])) {
for (i in 0..perm.count) {
var newPerm = perm.toList
newPerm.insert(i, toInsert)
}
}
return perms
}

var derange = Fn.new { |input|
if (input.isEmpty) return [input]
var perms = permute.call(input)
var derangements = []
for (perm in perms) {
var deranged = true
for (i in 0...perm.count) {
if (perm[i] == i) {
deranged = false
break
}
}
}
return derangements
}

var subFactorial // recursive
subFactorial = Fn.new { |n|
if (n == 0) return BigInt.one
if (n == 1) return BigInt.zero
return (subFactorial.call(n-1) + subFactorial.call(n-2)) * (n - 1)
}

var input = [0, 1, 2, 3]
var derangements = derange.call(input)
System.print("There are %(derangements.count) derangements of %(input), namely:\n")
System.print(derangements.join("\n"))

System.print("\nN  Counted   Calculated")
System.print("-  -------   ----------")
for (n in 0..9) {
var list = List.filled(n, 0)
for (i in 0...n) list[i] = i
var counted = derange.call(list).count
Fmt.print("\$d  \$-9d \$-9i", n, counted, subFactorial.call(n))
}
System.print("\n!20 = %(subFactorial.call(20))")
```
Output:
```There are 9 derangements of [0, 1, 2, 3], namely:

[1, 2, 3, 0]
[2, 0, 3, 1]
[2, 3, 0, 1]
[2, 3, 1, 0]
[1, 0, 3, 2]
[1, 3, 0, 2]
[3, 0, 1, 2]
[3, 2, 0, 1]
[3, 2, 1, 0]

N  Counted   Calculated
-  -------   ----------
0  1         1
1  0         0
2  1         1
3  2         2
4  9         9
5  44        44
6  265       265
7  1854      1854
8  14833     14833
9  133496    133496

!20 = 895014631192902121
```

## zkl

Translation of: Python

mostly

```fcn subFact(n){
if(n==0) return(1);
if(n==1) return(0);
(n-1)*(self.fcn(n-1) + self.fcn(n-2));
}

fcn derangements(n){
// All deranged permutations of the integers 0..n-1 inclusive
enum:=[0..n-1].pump(List);
Utils.Helpers.permuteW(enum).filter('wrap(perm){
perm.zipWith('==,enum).sum(0) == 0
});
}
fcn derangers(n){  // just count # of derangements
enum:=[0..n-1].pump(List);
Utils.Helpers.permuteW(enum).reduce('wrap(sum,perm){
sum + (perm.zipWith('==,enum).sum(0) == 0)
},0);
}```
```println("Derangements of 0,1,2,3:\n",derangements(4));
println("\nTable of n vs counted vs calculated derangements:");
foreach n in (10){
println("%2d %-6d %-6d".fmt(n, derangers(n), subFact(n)));
}

n:=20; println("\n!%d = %d".fmt(n, subFact(n)));```
Output:
```Derangements of 0,1,2,3:
L(L(3,0,1,2),L(2,0,3,1),L(2,3,0,1),L(3,2,0,1),L(3,2,1,0),
L(2,3,1,0),L(1,2,3,0),L(1,3,0,2),L(1,0,3,2))

Table of n vs counted vs calculated derangements:
0 1      1
1 0      0
2 1      1
3 2      2
4 9      9
5 44     44
6 265    265
7 1854   1854
8 14833  14833
9 133496 133496

!20 = 895014631192902121
```

Lazy/iterators version:

```fcn derangements(n){ //-->Walker
enum:=[0..n-1].pump(List);
Utils.Helpers.permuteW(enum).tweak('wrap(perm){
if(perm.zipWith('==,enum).sum(0)) Void.Skip
else perm
});
}
fcn derangers(n){  // just count # of derangements, w/o saving them
derangements(n).reduce('+.fpM("10-",1),0);  // ignore perm --> '+(1,sum)...
}```
```foreach d in (derangements(4)){ println(d) }
//rest of test code remains the same```