aoc_2024/day_2.c

#include "stdlib.h"
#include "stdio.h"
#include "string.h"

int numbers[2048*2048];
int sizes[2048];

int _is_safe(int n, int size, int* levels) {
  if(size <= 0) return 0;

  int current = -1;
  int direction = 0;

  for(int i = 0; i < size; i++) {
    if(i == n) continue;
    int next = levels[i];
    if(current == -1) {
      current = next;
    } else if(direction == 0 && (next < current && next >= current - 3)) {
      direction = 1;
    } else if(direction == 0 && (next > current && next <= current + 3)) {
      direction = 2;
    } else if(direction == 0) {
      return 0;
    } else if(direction == 1 && (next >= current || next < current - 3)) {
      return 0;
    } else if(direction == 2 && (next <= current || next > current + 3)) {
      return 0;
    }

    current = next;
  }

  return 1;
}

int is_safe(int size, int* levels) {
  for(int i = -1; i < size; i++) {
    if(_is_safe(i, size, levels)) return 1;
  }
  return 0;
}

int main(int argc, char* argv[]) {
  if(argc < 2) {
    fprintf(stderr, "Filename required\n");
    return 1;
  }

  FILE* file = fopen(argv[1], "r");
  if(file == NULL) {
    fprintf(stderr, "Could not open %s\n", argv[1]);
    return 2;
  }
  
  memset(numbers, 0, sizeof(numbers));
  char* line = NULL;
  size_t line_size = 0;
  int i = 0;
  while(getline(&line, &line_size, file) > 0) {
    char* save = NULL;
    char* token = strtok_r(line, " ", &save);
    if(token == NULL || token[0] == '\n' || token[0] == '\0') break;
    int j = 0;
    do {
      numbers[i*2048 + j] = atoi(token);
      j += 1;
    } while((token = strtok_r(NULL, " ", &save)));
    sizes[i] = j;
    i += 1;
  }
  free(line);

  int safe = 0;
  for(i = 0; i < 2048; i++) {
    if(sizes[i] == 0) continue;
    if(is_safe(sizes[i], &numbers[2048*i])) {
      safe += 1;
    }
  }

  fprintf(stdout, "Safe: %d\n", safe);

  return 0;
}