adventofcode2024/day2/c/day2.c

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

#define CHARS_MAX 64
#define MAX_LEVELS 16
#define abs(a) ((a) < 0 ? (-(a)) : (a))

int is_safe(int *levels, int level_count);

int main() {
    char *p, *buf, c;

    buf = calloc(CHARS_MAX, sizeof(char));
    p = buf;
    int safes1 = 0, safes2 = 0;

    int levels[MAX_LEVELS], level_count = 0;
    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c != '\n') {
            continue;
        }
        p = buf;
        int level = 0;

        p--;
        do {
            p++;
            sscanf(p, "%i", &levels[level_count]);
            level_count++;
            while (*p != ' ' && *p != '\n') p++;
        } while(*p != '\n');

        if (is_safe(levels, level_count)) {
            safes1++;
        }

        int new_levels[MAX_LEVELS];
        for (int i = 0; i < level_count; i++) {
            memcpy(new_levels, levels, level_count * sizeof(levels[0]));
            for (int j = i; j < level_count - 1; j++) {
                new_levels[j] = levels[j+1];
            }

            if (is_safe(new_levels, level_count - 1)) {
                safes2++;
                break;
            }
        }

        memset(buf, 0, CHARS_MAX);
        p = buf;
        level_count = 0;
    }

    free(buf);

    printf("%i\n", safes1);
    printf("%i\n", safes2);
}

int is_safe(int *levels, int level_count) {
    int diff = 0, safe = 1;
    for (int i = 0; i < level_count; i++) {
        if (i != 0) {
            if (abs(levels[i] - levels[i-1]) < 1 || abs(levels[i] - levels[i-1]) > 3) {
                safe = 0;
            }

            if ((levels[i] - levels[i-1]) * diff < 0) {
                safe = 0;
            }

            diff = levels[i] - levels[i-1];
        }
    }

    return safe;
}