2017/advent13.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
   8 int main(void)
   9 {
  10   int severity = 0;
  11   int count = 0;
  12   int layer;
  13   int depth;
  14   int list[100] = {0}; // cheat based on pre-inspecting input
  15   int max = 0;
  16   while (scanf("%d: %d\n", &layer, &depth) == 2) {
  17     count++;
  18     max = layer;
  19     list[layer] = depth;
  20   }
  21   printf ("read %d items, max layer %d\n", count, max);
  22   int delay = -1;
  23   while (1) {
  24     delay++;
  25     int i;
  26     for (i = 0; i <= max; i++) {
  27       if (!list[i])
  28         continue;
  29       int cycle = (list[i] - 1) * 2;
  30       if (! ((i + delay) % cycle)) {
  31         // printf (" delay %d, i %d, cycle %d\n", delay, i, cycle);
  32         if (!delay)
  33           severity += i * list[i];
  34         else
  35           break;
  36       }
  37     }
  38     if (delay && i > max)
  39       break;
  40   }
  41   printf ("with no delay, severity is %d\n", severity);
  42   printf ("delay %d to avoid collisions\n", delay);
  43   return 0;
  44 }