2018/day14a.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <stdarg.h>
   6 #include <stdbool.h>
   7 #include <inttypes.h>
   8 #include <assert.h>
   9
  10 bool debug(const char *fmt, ...) {
  11   va_list ap;
  12   if (getenv("DEBUG")) {
  13     va_start(ap, fmt);
  14     vfprintf(stderr, fmt, ap);
  15     va_end(ap);
  16     return true;
  17   }
  18   return false;
  19 }
  20
  21 #define LIMIT 200000
  22
  23 static char list[LIMIT] = "37";
  24
  25 static void dump(int iter, int size, int idx1, int idx2) {
  26   if (!debug("iter %d:", iter))
  27     return;
  28   for (int i = 0; i < size; i++)
  29     if (i == idx1)
  30       debug("(%c)", list[i]);
  31     else if (i == idx2)
  32       debug("[%c]", list[i]);
  33     else
  34       debug(" %c", list[i]);
  35   debug("\n");
  36 }
  37
  38 int main(int argc, char **argv) {
  39   int goal = 77201;
  40   int max;
  41   int size = 2;
  42   int idx1 = 0;
  43   int idx2 = 1;
  44   int iter = 0;
  45
  46   if (argc > 1)
  47     goal = atoi(argv[1]);
  48   if (argc > 2)
  49     max = atoi(argv[2]);
  50   else
  51     max = goal + 12;
  52   if (goal > max - 11) {
  53     fprintf(stderr, "recompile with larger limit to hit goal of %d\n", goal);
  54     exit(1);
  55   }
  56
  57   while (size < max) {
  58     dump(iter++, size, idx1, idx2);
  59     size += sprintf(list + size, "%d", list[idx1] - '0' + list[idx2] - '0');
  60     idx1 = (list[idx1] - '0' + idx1 + 1) % size;
  61     idx2 = (list[idx2] - '0' + idx2 + 1) % size;
  62     if (size % 1000 < 2)
  63       printf("%d...\n", size);
  64   }
  65   dump(iter, size, idx1, idx2);
  66   printf("score: %.10s\n", list + goal);
  67   return 0;
  68 }