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From: fir <fir@grunge.pl>
Newsgroups: comp.lang.c
Subject: Re: Recursion, Yo
Date: Sun, 07 Apr 2024 11:52:29 +0200
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Lawrence D'Oliveiro wrote:
> Some homies they be sayin’ recursion is Teh Evulz. Well, check this
> out. This program be recursing to the max, yo.
>
> Peace.
>
> ----
> /*
>      Generate permutations of a list of items.
>      Pass a list of arbitary words as command arguments, and this
>      program will print out all possible orderings of them.
> */
>
> #include <iso646.h>
> #include <stdbool.h>
> #include <stdlib.h>
> #include <stdio.h>
>
> typedef void (*permute_action)
>    (
>      const char * const * words
>    );
>
> void permute
>    (
>      unsigned int nrwords,
>      const char * const * words,
>      permute_action action
>    )
>    {
>      if (nrwords > 0)
>        {
>          const char ** const permbuf = (const char **)malloc(nrwords * sizeof(char *));
>          bool * const used = (bool *)malloc(nrwords);
>          for (unsigned int i = 0; i < nrwords; ++i)
>            {
>              used[i] = false;
>            } /*for*/
>
>          void permute1
>            (
>              unsigned int depth
>            )
>            {
>              if (depth < nrwords)
>                {
>                  for (unsigned int i = 0; i < nrwords; ++i)
>                    {
>                      if (not used[i])
>                        {
>                          permbuf[depth] = words[i];
>                          used[i] = true;
>                          permute1(depth + 1);
>                          used[i] = false;
>                        } /*if*/
>                    } /*for*/
>                }
>              else
>                {
>                  action(permbuf);
>                } /*if*/
>            } /*permute1*/
>
>          permute1(0);
>
>          free(permbuf);
>          free(used);
>        } /*if*/
>    } /*permute*/
>
> int main
>    (
>      int argc,
>      char ** argv
>    )
>    {
>      const unsigned int nrwords = argc - 1;
>      unsigned int count = 0;
>
>      void collect
>        (
>          const char * const * words
>        )
>        {
>          count += 1;
>          fprintf(stdout, "[%d](", count);
>          for (unsigned int i = 0; i < nrwords; ++i)
>            {
>              if (i != 0)
>                {
>                  fputs(", ", stdout);
>                } /*if*/
>              fputs(words[i], stdout);
>            } /*for*/
>          fputs(")\n", stdout);
>        } /*collect*/
>
>      permute
>        (
>          /*nrwords =*/ nrwords,
>          /*words =*/ (const char * const * )(argv + 1),
>          /*permute_action =*/ (permute_action)collect
>        );
>
>      fprintf(stdout, "Nr found: %d\n", count);
>    } /*main*/
>
okay, there are some class of things that suit good for recursion - and 
its probably good to spot whose they are