2016/advent4.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 #include <ctype.h>
   8
   9 int main(void)
  10 {
  11   ssize_t nread;
  12   size_t len = 0;
  13   char *line = NULL;
  14   int sum = 0;
  15   while ((nread = getline(&line, &len, stdin)) >= 0) {
  16     line[nread - 1] = '\0';
  17     int freq[26] = { 0 };
  18     int count = 0;
  19     int id = 0;
  20     char *p = line;
  21     while (*p != '[') {
  22       if (isalpha (*p)) {
  23         freq[*p - 'a']++;
  24         if (freq[*p - 'a'] > count)
  25           count = freq[*p - 'a'];
  26       } else if (isdigit (*p))
  27         id = id * 10 + *p - '0';
  28       p++;
  29     }
  30     p++;
  31     for (int i = 0; *p != ']'; i++) {
  32       if (i == 26) {
  33         count--;
  34         i = 0;
  35       }
  36       if (freq[i] == count)
  37         if (*p++ != i + 'a') {
  38           id = 0;
  39           if (getenv ("DEBUG"))
  40             printf ("room %s is bogus\n", line);
  41           break;
  42         }
  43     }
  44     if (*p == ']') {
  45       if (getenv ("DEBUG"))
  46         printf ("room %s is valid\n", line);
  47       p = line;
  48       while (!isdigit (*p)) {
  49         if (*p == '-')
  50           *p = ' ';
  51         else
  52           *p = 'a' + (*p - 'a' + id) % 26;
  53         p++;
  54       }
  55       *p = '\0';
  56       printf ("valid rooms include %d: %s\n", id, line);
  57     }
  58     sum += id;
  59   }
  60   printf ("sum of ids is %d\n", sum);
  61   return 0;
  62 }