2017/advent17.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <unistd.h>
   6 #include <stdint.h>
   7
   8 int main(int argc, char **argv)
   9 {
  10   int step = 328;
  11   if (argc == 2)
  12     step = atoi (argv[1]);
  13   int len = 1;
  14   int value = 0;
  15   int cur = 0;
  16   for (int i = 1; i <= 50000000; i++) {
  17     if (!(i % 10000))
  18       printf ("\b\b\b\b\b\b\b\b\b%9d", i), fflush (stdout);
  19     int next = (cur + step) % len;
  20     if (!next)
  21       value = i;
  22     len++;
  23     cur = next + 1;
  24     if (getenv ("DEBUG") && i < 10) {
  25       printf ("iter %d: cur/len is %d/%d, val after 0 is %d\n", i, cur, len,
  26               value);
  27     }
  28   }
  29   printf ("\nnext is %d\n", value);
  30   return 0;
  31 }