29 lines
2.4 KiB
Rexx
29 lines
2.4 KiB
Rexx
/*REXX pgm finds one or more missing permutations from an internal list & displays them.*/
|
|
list= 'ABCD CABD ACDB DACB BCDA ACBD ADCB CDAB DABC BCAD CADB CDBA CBAD ABDC ADBC BDCA',
|
|
"DCBA BACD BADC BDAC CBDA DBCA DCAB" /*list that is missing one permutation.*/
|
|
@.= /* [↓] needs to be as 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*/ /* [↑] build a letter array for speed.*/
|
|
call permSet 1 /*invoke PERMSET subroutine recursively*/
|
|
exit /*stick a fork in it, we're all done. */
|
|
/*──────────────────────────────────────────────────────────────────────────────────────*/
|
|
permSet: procedure expose $. @. bunch list things; parse arg ? /*calls self recursively.*/
|
|
if ?>bunch then do; _=
|
|
do m=1 for bunch /*build a permutation. */
|
|
_= _ || @.m /*add permutation──►list.*/
|
|
end /*m*/
|
|
/* [↓] is in the list? */
|
|
if wordpos(_,list)==0 then say _ ' is missing from the list.'
|
|
end
|
|
else do x=1 for things /*build a permutation. */
|
|
do k=1 for ?-1
|
|
if @.k==$.x then iterate x /*was permutation built? */
|
|
end /*k*/
|
|
@.?= $.x /*define as being built. */
|
|
call permSet ?+1 /*call self recursively. */
|
|
end /*x*/
|
|
return
|