29 lines
2.3 KiB
Rexx
29 lines
2.3 KiB
Rexx
/*REXX pgm finds one or more missing permutations from an internal list & displays them.*/
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list = 'ABCD CABD ACDB DACB BCDA ACBD ADCB CDAB DABC BCAD CADB CDBA',
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'CBAD ABDC ADBC BDCA DCBA BACD BADC BDAC CBDA DBCA DCAB'
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@.= /* [↓] needs to be as long as THINGS.*/
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@abcU = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ' /*an uppercase (Latin/Roman) alphabet. */
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things = 4 /*number of unique letters to be used. */
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bunch = 4 /*number letters to be used at a time. */
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do j=1 for things /* [↓] only get a portion of alphabet.*/
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$.j=substr(@abcU,j,1) /*extract just one letter from alphabet*/
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end /*j*/ /* [↑] build a letter array for speed.*/
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call permSet 1 /*invoke PERMSET subroutine recursively*/
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exit /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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permSet: procedure expose $. @. bunch list things; parse arg ?
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if ?>bunch then do; _=
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do m=1 for bunch /*build a permutation. */
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_=_ || @.m /*add permutation──►list.*/
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end /*m*/
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/* [↓] is in the list? */
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if wordpos(_,list)==0 then say _ ' is missing from the list.'
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end
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else do x=1 for things /*build a permutation. */
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do k=1 for ?-1
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if @.k==$.x then iterate x /*was permutation built? */
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end /*k*/
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@.?=$.x /*define as being built. */
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call permSet ?+1 /*call subr. recursively.*/
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end /*x*/
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return
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