2016/advent15.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6
   7 #define MAX 7 // cheat, by pre-inspecting input
   8
   9 int
  10 main (int argc, char **argv)
  11 {
  12   int sizes[MAX] = { 0 };
  13   int offsets[MAX] = { 0 };
  14   ssize_t nread;
  15   size_t len = 0;
  16   char *line = NULL;
  17   int count = 0;
  18   while ((nread = getline(&line, &len, stdin)) >= 0) {
  19     char *p = strstr (line, "has") + 3;
  20     sizes[count] = atoi (p);
  21     p = strstr (line, "at position") + 11;
  22     offsets[count] = atoi (p);
  23     count++;
  24   }
  25   sizes[count++] = 11;
  26   printf ("read/synthesized details for %d discs\n", count);
  27   int time = -1;
  28  retry:
  29   time++;
  30   for (int i = 0; i < count; i++)
  31     if ((time + offsets[i] + i) % sizes[i])
  32       goto retry;
  33   printf ("start at time %d\n", time - 1);
  34   return 0;
  35 }