2016/advent10.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6 #include <stdbool.h>
   7 #include <ctype.h>
   8
   9 // cheat by pre-inspecting: all values and bots between 0 and 255 exclusive
  10 #define MAX 255
  11 typedef struct bot bot;
  12 struct bot {
  13   unsigned char v1;
  14   unsigned char v2;
  15   unsigned char lo;
  16   unsigned char hi;
  17   bool out_lo;
  18   bool out_hi;
  19   bool done;
  20 } bots[MAX];
  21 unsigned char out[MAX];
  22
  23 int main(int argc, char **argv)
  24 {
  25   ssize_t nread;
  26   size_t len = 0;
  27   char *line = NULL;
  28   int inputs = 0;
  29   int tasks = 0;
  30   while ((nread = getline(&line, &len, stdin)) >= 0) {
  31     if (*line == 'v') {
  32       int v, b;
  33       inputs++;
  34       if (sscanf (line, "value %d goes to bot %d\n", &v, &b) != 2)
  35         return 1;
  36       if (bots[b].v1)
  37         bots[b].v2 = v;
  38       else
  39         bots[b].v1 = v;
  40     } else {
  41       int b0, b1, b2;
  42       char t1, t2;
  43       tasks++;
  44       if (sscanf (line, "bot %d gives low to %c%*s %d and high to %c%*s %d\n",
  45                   &b0, &t1, &b1, &t2, &b2) != 5)
  46         return 1;
  47       if (t1 == 'o')
  48         bots[b0].out_lo = true;
  49       if (t2 == 'o')
  50         bots[b0].out_hi = true;
  51       bots[b0].lo = b1;
  52       bots[b0].hi = b2;
  53     }
  54   }
  55   printf ("%d inputs are sorted among %d bots\n", inputs, tasks);
  56   bool change = true;
  57   int goal = 0;
  58   int iter = 0;
  59   while (change) {
  60     printf (" iteration %d\n", iter++);
  61     change = false;
  62     for (int i = 0; i < MAX; i++)
  63       if (!bots[i].done && bots[i].v1 && bots[i].v2) {
  64         printf ("tracing bot %d, v1 %d, v2 %d, lo %d, hi %d\n",
  65                 i, bots[i].v1, bots[i].v2, bots[i].lo, bots[i].hi);
  66         bots[i].done = change = true;
  67         if (bots[i].v1 > bots[i].v2) {
  68           unsigned char tmp = bots[i].v1;
  69           bots[i].v1 = bots[i].v2;
  70           bots[i].v2 = tmp;
  71         }
  72         unsigned char *l, *h;
  73         if (bots[i].out_lo)
  74           l = &out[bots[i].lo];
  75         else if (bots[bots[i].lo].v1)
  76           l = &bots[bots[i].lo].v2;
  77         else
  78           l = &bots[bots[i].lo].v1;
  79         if (bots[i].out_hi)
  80           h = &out[bots[i].hi];
  81         else if (bots[bots[i].hi].v1)
  82           h = &bots[bots[i].hi].v2;
  83         else
  84           h = &bots[bots[i].hi].v1;
  85         *l = bots[i].v1;
  86         *h = bots[i].v2;
  87         if (bots[i].v1 == 17 && bots[i].v2 == 61)
  88           goal = i;
  89       }
  90   }
  91   printf ("values 17 and 61 are compared by bot %d\n", goal);
  92   printf ("first three outputs have product %d\n", out[0] * out[1] * out[2]);
  93   return 0;
  94 }