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Re: Cookies in boxes - algorithmic challenge

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From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: Cookies in boxes - algorithmic challenge
Date Thu, 09 Apr 2026 17:07:25 -0700
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Michael S <already5chosen@yahoo.com> writes:

> On Wed, 1 Apr 2026 16:34:47 +0300
> Michael S <already5chosen@yahoo.com> wrote:
>
> <snip>
>
> My solution #2.
> That is my own, with no proof preceding code.  It went in other direction
> - from hacking the code to proving it later.
> It is pretty fast.  Can be made faster yet by replication of some code
> and re-arrangement in the find() routine, but for purposes of
> illustration I wanted it short.

Just fyi..  I did some speed comparisons between the code below and
the compatible solver that I wrote.  Your code is faster, scales
better, and also has better worst-case behavior (which is to say
that my code has worse worst-case behavior).  So I think the timing
numbers I was seeing before may have been just the result of being
lucky in the draw of random numbers.

> #include <stdint.h>
> #include <string.h>
> #include <stdbool.h>
>
> #include "solver.h"
>
> static
> uint8_t solver_find(
>   const uint8_t b_idx[N_BOXES][N_BOXES],
>   uint8_t       result[N_BOXES],
>   const uint8_t free[N_BOXES],
>   int           n_free,
>   uint8_t       v,
>   const uint8_t bx[N_BOXES][BOX_SIZE])
> {
>   typedef struct {
>     uint8_t parent, bi;
>   } db_rec;
>   db_rec db[N_BOXES];
>   bool valid[N_BOXES] = {0};
>   uint8_t que[N_BOXES], *wr = que, *rd = que;
>
>   valid[v] = true;
>   *wr++ = v;
>   for (;;) {
>     uint8_t vv = *rd++;
>     for (int i = 0; i < n_free; ++i) {
>       uint8_t bi = free[i];
>       uint8_t ci = b_idx[bi][vv];
>       if (ci != BOX_SIZE) {
>         result[bi] = ci;
>         while (vv != v) {
>           bi = db[vv].bi;
>           vv = db[vv].parent;
>           result[bi] = b_idx[bi][vv];
>         };
>         return i;
>       }
>     }
>     // add neighbors to database
>     for (int bi = 0; bi < N_BOXES; ++bi) {
>       if (b_idx[bi][vv] != BOX_SIZE) {
>         uint8_t a = bx[bi][result[bi]];
>         if (!valid[a]) {
>           valid[a] = true;
>           db[a] = (db_rec){ .parent = vv, .bi = bi };
>           *wr++ = a;
>         }
>       }
>     }
>   }
> }
>
> peek_t solver(boxes_t boxes)
> {
>   // build index
>   uint8_t b_idx[N_BOXES][N_BOXES];
>   memset(b_idx, BOX_SIZE, sizeof(b_idx));
>   for (int bi = 0; bi < N_BOXES; ++bi) {
>     for (int ci = 0; ci < BOX_SIZE; ++ci) {
>       uint8_t v = boxes.b[bi][ci];
>       if (b_idx[bi][v] == BOX_SIZE)
>         b_idx[bi][v] = ci;
>     }
>   }
>
>   uint8_t free_boxes[N_BOXES];
>   for (int bi = 0; bi < N_BOXES; ++bi)
>     free_boxes[bi] = bi;
>   int n_free = N_BOXES;
>
>   peek_t result = {0};
>   bool used_sorts[N_BOXES]={0};
>   while (n_free > 0) {
>     int bi =  free_boxes[--n_free]; // new set
>     result.b[bi] = 0;
>     uint8_t v = boxes.b[bi][0];
>     used_sorts[v] = true;
>     uint8_t pend_que[N_BOXES],
>        *pend_wr = pend_que, *pend_rd = pend_que;
>     *pend_wr++ = bi;
>     while (pend_wr != pend_rd && n_free != 0) {
>       int bk = *pend_rd++;
>       for (int ci = 0; ci < BOX_SIZE; ++ci) {
>         v = boxes.b[bk][ci];
>         if (!used_sorts[v]) {
>           // new value in set
>           uint8_t v_fi = solver_find(
>                           b_idx, result.b, free_boxes,
>                           n_free, v, boxes.b);
>           uint8_t v_bi = free_boxes[v_fi];
>           used_sorts[v] = true;
>           *pend_wr++ = v_bi;
>           free_boxes[v_fi] = free_boxes[--n_free];
>               // remove from free  list
>         }
>       }
>     }
>   }
>   return result;
> }

I think I could eventually understand what this code is doing, and
after that get a sense of how and why it works.  In its current
form I think that would take me a fair amount of time.  It would
help to have a roadmap, more evocative names, more functional
decomposition, or ideally all three.  Please understand, I'm not
asking or suggesting you do anything;  my intention is only to
provide feedback that may be of some benefit to you.

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Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-01 16:34 +0300
  Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-01 10:02 -0400
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-01 17:15 +0300
      Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-01 10:28 -0400
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-01 17:58 +0300
  Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-01 15:20 +0100
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-01 17:56 +0300
      Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-01 19:50 +0100
        Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-01 15:56 -0400
          Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-01 23:33 +0100
        Re: Cookies in boxes - algorithmic challenge Richard Harnden <richard.nospam@gmail.invalid> - 2026-04-04 07:43 +0100
          Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-04 11:54 +0100
  Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-01 15:24 -0400
  Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-01 17:24 -0400
    Re: Cookies in boxes - algorithmic challenge Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-04-02 16:25 +0100
      Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-02 17:10 +0100
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-02 22:19 +0300
      Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-02 13:03 -0400
        Re: Cookies in boxes - algorithmic challenge Richard Harnden <richard.nospam@gmail.invalid> - 2026-04-02 18:52 +0100
        Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-02 19:50 +0100
          Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-02 22:24 +0300
        Re: Cookies in boxes - algorithmic challenge Mike Terry <news.dead.person.stones@darjeeling.plus.com> - 2026-04-02 20:13 +0100
          Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-02 22:36 +0300
      Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-02 22:14 +0300
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-02 22:10 +0300
      Re: Cookies in boxes - algorithmic challenge Tristan Wibberley <tristan.wibberley+netnews2@alumni.manchester.ac.uk> - 2026-04-06 22:36 +0100
        Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-06 15:42 -0700
        Re: Cookies in boxes - algorithmic challenge Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-04-06 15:44 -0700
  Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-04 13:33 -0400
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-04 21:03 +0300
      Re: Cookies in boxes - algorithmic challenge DFS <nospam@dfs.com> - 2026-04-04 14:19 -0400
      Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-04 20:22 +0100
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-04 22:40 +0300
  Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-04 17:08 -0700
  Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-08 08:42 -0700
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-08 22:23 +0300
      Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-09 21:22 -0700
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-10 12:23 +0300
          Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-10 22:41 -0700
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-10 16:16 +0300
          Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-11 04:27 -0700
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-11 22:56 +0300
          Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-11 15:57 -0700
            Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-12 02:15 +0300
            Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-13 02:03 +0300
            Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-13 17:11 +0300
              Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-16 23:52 -0700
                Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-17 14:44 +0300
                Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-17 07:40 -0700
                Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-17 18:30 +0300
                Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-20 00:43 +0300
                Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-21 20:37 +0300
                Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-21 18:22 -0700
                Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-22 12:05 +0300
                Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-29 06:55 -0700
    Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-15 02:15 +0300
      Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-16 02:57 -0700
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-17 17:04 +0300
  Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-08 23:45 +0300
    Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-09 16:37 -0700
      Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-10 17:02 +0300
        Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-11 03:45 -0700
  Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-09 00:01 +0300
    Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-09 17:07 -0700
      Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-10 18:06 +0300
        Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-11 04:31 -0700
        Re: Cookies in boxes - algorithmic challenge Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-04-16 03:22 -0700
  Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-17 17:58 +0200
    Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-17 18:08 +0200
    Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-17 17:47 +0100
      Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-17 19:24 +0200
    Re: Cookies in boxes - algorithmic challenge scott@slp53.sl.home (Scott Lurndal) - 2026-04-17 19:58 +0000
      Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-18 05:52 +0200
        Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-18 11:53 +0100
          Re: Cookies in boxes - algorithmic challenge Bart <bc@freeuk.com> - 2026-04-18 12:04 +0100
        Re: Cookies in boxes - algorithmic challenge Michael S <already5chosen@yahoo.com> - 2026-04-18 20:35 +0300
  Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-17 19:52 +0200
    Re: Cookies in boxes - algorithmic challenge Bonita Montero <Bonita.Montero@gmail.com> - 2026-04-17 20:17 +0200

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