2018/day2b.c

   1 #define _GNU_SOURCE 1
   2 #include <stdio.h>
   3 #include <string.h>
   4 #include <stdlib.h>
   5 #include <stdarg.h>
   6
   7 void debug(const char *fmt, ...) {
   8   va_list ap;
   9   if (getenv("DEBUG")) {
  10     va_start(ap, fmt);
  11     vfprintf(stderr, fmt, ap);
  12     va_end(ap);
  13   }
  14 }
  15
  16 static void compare(const char *a, const char *b) {
  17   const char *p = a, *q = b;
  18   int diff = 0;
  19   while (*p) {
  20     if (*p != *q)
  21       diff++;
  22     p++;
  23     q++;
  24   }
  25   debug(" comparing %s and %s: %d\n", a, b, diff);
  26   if (diff == 1) {
  27     printf("Nearby: %s"
  28            "        %s", a, b);
  29     exit(0);
  30   }
  31 }
  32
  33 int main(int argc, char **argv) {
  34   char **list = NULL;
  35   size_t size = 0, len = 0;
  36   char *line;
  37   size_t i, j;
  38
  39   if (argc > 1)
  40     stdin = freopen(argv[1], "r", stdin);
  41
  42   while (getline(&line, &len, stdin) >= 0) {
  43     list = reallocarray(list, ++size, sizeof *list);
  44     list[size - 1] = strdup(line);
  45   }
  46   printf("read %zd lines\n", size);
  47   for (i = 0; i < size; i++)
  48     for (j = i + 1; j < size; j++)
  49       compare(list[i], list[j]);
  50   printf("no nearby found\n");
  51   return 1;
  52 }