advent_of_code/day_2/1.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

#define BUFFER_SIZE 1024

typedef struct levels {
  size_t mem_size;
  size_t size;
  int *data;
} levels_t;

int main(void) {
  FILE *fp = fopen("input", "r");

  if (fp == NULL) {
    perror("input");
    return 1;
  }

  char buffer[BUFFER_SIZE];

  levels_t levels;
  levels.mem_size = 10;
  levels.size = 0;
  levels.data = malloc(sizeof(unsigned int) * levels.mem_size);

  unsigned int sum = 0;
  while (fgets(buffer, BUFFER_SIZE, fp) != NULL) {
    char *next = strtok(buffer, " ");

    while (next != NULL) {
      if (levels.size >= levels.mem_size) {
        levels.mem_size *= 2;
        levels.data =
            realloc(levels.data, levels.mem_size * sizeof(unsigned int));
      }

      sscanf(next, "%d", &levels.data[levels.size]);
      levels.size++;

      next = strtok(NULL, " ");
    }

    bool safe = true;
    int diff = levels.data[1] - levels.data[0];
    int increasing = diff > 0 ? 1 : -1;
    for (size_t i = 1; i < levels.size; i++) {
      diff = increasing * (levels.data[i] - levels.data[i - 1]);

      if (diff < 1 || diff > 3) {
        safe = false;
        break;
      }
    }

    if (safe) {
      sum++;
    }

    levels.size = 0;
  }

  free(levels.data);

  printf("%u\n", sum);

  fclose(fp);

  return 0;
}