Find the missing permutation: Difference between revisions

<lang rexx>/*REXX program finds (a)one or more missing permutation(s)permutations from an internal list.*/

list = 'ABCD CABD ACDB DACB BCDA ACBD ADCB CDAB DABC BCAD CADB CDBA',

'CBAD ABDC ADBC BDCA DCBA BACD BADC BDAC CBDA DBCA DCAB'

@.= /* [↓] needs to be THINGSas long. as THINGS.*/

@abcU = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' /*an uppercase (Latin/Roman) alphabet. */

things = 4 /*#number of unique letters to be used. */

bunch = 4 /*#number letters to be used at a time. */

do j=1 for things /* [↓] only get a portion of alphabet.*/

$.j=substr(@abcU,j,1) /*extract just one letter from alphabet*/

end /*j*/ /* [↑] constructbuild a letter array for speed.*/

call permsetpermSet 1 /*invoke PERMSET sub. (recursively). */

exit /*stick a fork in it, we're all done. */

permsetpermSet: procedure expose $. @. bunch list things; parse arg ?

_=; do m=1 for bunch /*build a permutation. */

_=_ || @.m /*add perm ──► listpermutation──►list*/

end /*m*/

/* [↓] is in the list? */

if wordpos(_,list)==0 then say _ ' is missing from the list.'

else do x=1 for things /*build a new permpermutation. */

if @.k==$.x then doiterate x k=1 /*was forpermutation built?-1*/

if @.k==$.x then iterate x end /*been built?k*/

@.?=$.x end /*kdefine as being built.*/

@.?=$.x call permSet ?+1 /*define ascall builtsubr. recursively*/