2018/day4b.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
   8 void debug(const char *fmt, ...) {
   9   va_list ap;
  10   if (getenv("DEBUG")) {
  11     va_start(ap, fmt);
  12     vfprintf(stderr, fmt, ap);
  13     va_end(ap);
  14   }
  15 }
  16
  17 #define LIMIT 3500
  18
  19 short array[LIMIT][60];
  20 char list[LIMIT];
  21
  22 static void process(int guard, int start, int end) {
  23   debug("processing %d: %d-%d\n", guard, start, end);
  24   for (int i = start; i < end; i++)
  25     array[guard][i]++;
  26 }
  27
  28 int main(int argc, char **argv) {
  29   size_t len = 0, count = 0;
  30   char *line;
  31   int i, j;
  32   int guard;
  33   int sleep, wake;
  34   char *p;
  35   bool pair = false;
  36
  37   if (argc > 1)
  38     if (!(stdin = freopen(argv[1], "r", stdin))) {
  39       perror("failure");
  40       exit(2);
  41     }
  42
  43   while (getline(&line, &len, stdin) >= 0) {
  44     count++;
  45     if (pair) {
  46       p = strchr(line, ':');
  47       if (!p) {
  48         fprintf(stderr, "bad input\n");
  49         exit(1);
  50       }
  51       wake = (p[1] - '0') * 10 + p[2] - '0';
  52       process(guard, sleep, wake);
  53       pair = false;
  54     } else {
  55       p = strchr(line, '#');
  56       if (p) {
  57         if (sscanf(p, "#%d ", &guard) != 1) {
  58           fprintf(stderr, "bad input\n");
  59           exit(1);
  60         }
  61         if (guard >= LIMIT) {
  62           printf("recompile with larger LIMIT!\n");
  63           exit(1);
  64         }
  65         list[guard]++;
  66       } else {
  67         p = strchr(line, ':');
  68         if (!p) {
  69           fprintf(stderr, "bad input\n");
  70           exit(1);
  71         }
  72         sleep = (p[1] - '0') * 10 + p[2] - '0';
  73         pair = true;
  74       }
  75     }
  76   }
  77   printf("read %zd lines\n", count);
  78   int best_guard = 0;
  79   int total_sleep = 0;
  80   int best_minute = 0;
  81   for (i = 0; i < LIMIT; i++) {
  82     int local_minute = 0;
  83     int local_sleep = 0;
  84     if (!list[i])
  85       continue;
  86     for (j = 0; j < 60; j++) {
  87       local_sleep += array[i][j];
  88       if (array[i][j] > array[i][local_minute])
  89         local_minute = j;
  90     }
  91     debug("guard %d slept %d best minute %d: %d\n", i, local_sleep,
  92           local_minute, array[i][local_minute]);
  93     if (array[i][local_minute] > total_sleep) {
  94       total_sleep = array[i][local_minute];
  95       best_guard = i;
  96       best_minute = local_minute;
  97     }
  98   }
  99   printf("best guard %d at minute %d = %d\n", best_guard, best_minute,
 100          best_guard * best_minute);
 101   return 0;
 102 }