2019/day4.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 <limits.h>
   8
   9 static int do_debug = -1;
  10 void debug(const char *fmt, ...) {
  11   va_list ap;
  12   if (do_debug < 0)
  13     do_debug = !!getenv("DEBUG");
  14   if (do_debug > 0) {
  15     va_start(ap, fmt);
  16     vfprintf(stderr, fmt, ap);
  17     va_end(ap);
  18   }
  19 }
  20
  21 void check(int i, int *a, int *b) {
  22   char buf[8];
  23   char count[10] = "";
  24   int j;
  25   bool pair = false;
  26
  27   if (snprintf(buf, sizeof buf, "0%d", i) != 7) {
  28     printf("invalid input %d\n", i);
  29     exit(1);
  30   }
  31   for (j = 1; j < 7; j++) {
  32     if (buf[j] < buf[j-1])
  33       return;
  34     count[buf[j] - '0']++;
  35   }
  36   for (j = 0; j < 10; j++) {
  37     if (count[j] > 1) {
  38       pair = true;
  39       if (count[j] == 2) {
  40         ++*b;
  41         break;
  42       }
  43     }
  44   }
  45   if (pair)
  46     ++*a;
  47 }
  48
  49 int main(int argc, char **argv) {
  50   int low = 158126, high = 624574;
  51   int i, count1 = 0, count2 = 0, possible = 0;
  52
  53   if (argc > 1)
  54     high = low = atoi(argv[1]);
  55   if (argc > 2)
  56     high = atoi(argv[2]);
  57
  58   for (i = low; i <= high; i++, possible++)
  59     check(i, &count1, &count2);
  60   printf("%d / %d possibilities over %d in range\n", count1, count2, possible);
  61   return 0;
  62 }