adventofcode2023/day22/c/day22.c

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

#define LINE_MAX_LENGTH 256
#define MAX_BRICKS 2048
#define NUM_0_CHARCODE 48
#define NUM_9_CHARCODE NUM_0_CHARCODE + 9
#define max(a,b) ((a) > (b) ? (a) : (b))
#define min(a,b) ((a) < (b) ? (a) : (b))
#define in_range(c,a,b) ((c) <= max(a,b) && (c) >= min(a,b))

typedef struct corner {
    int x;
    int y;
    int z;
} corner_t;

typedef struct brick {
    corner_t corners[2];
    int fallen;
} brick_t;

int fall(brick_t bricks[], int bricks_num);
int intersect(brick_t brick_a, brick_t brick_b);

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

    buf = (char *)malloc(LINE_MAX_LENGTH);
    memset(buf, 0, LINE_MAX_LENGTH);
    p = buf;

    brick_t bricks[MAX_BRICKS];
    int bricks_num = 0;

    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c == '\n') {
            p = buf;
            sscanf(p, "%i", &bricks[bricks_num].corners[0].x);
            while (*p != ',') p++;
            p++;
            sscanf(p, "%i", &bricks[bricks_num].corners[0].y);
            while (*p != ',') p++;
            p++;
            sscanf(p, "%i", &bricks[bricks_num].corners[0].z);
            while (*p != '~') p++;
            p++;
            sscanf(p, "%i", &bricks[bricks_num].corners[1].x);
            while (*p != ',') p++;
            p++;
            sscanf(p, "%i", &bricks[bricks_num].corners[1].y);
            while (*p != ',') p++;
            p++;
            sscanf(p, "%i", &bricks[bricks_num].corners[1].z);
            bricks_num++;
            memset(buf, 0, LINE_MAX_LENGTH);
            p = buf;
        }
    }

    
    while (fall(bricks, bricks_num));
    for (int i = 0; i < bricks_num; i++) {
        bricks[i].fallen = 0;
    }

    int part1 = 0;
    int part2 = 0;
#pragma omp parallel for schedule(dynamic)
    for (int i = 0; i < bricks_num; i++) {
        brick_t bricks_copy[MAX_BRICKS];
        memcpy(bricks_copy, bricks, sizeof(bricks));
        bricks_copy[i].corners[0].z = 0;
        bricks_copy[i].corners[1].z = 0;
        int fallen = 0;
        while (fall(bricks_copy, bricks_num));
        for (int j = 0; j < bricks_num; j++) {
            fallen += bricks_copy[j].fallen;
        }
#pragma omp critical
        {
            if (fallen == 0) {
                part1++;
            }
            part2 += fallen;
        }
    }

    printf("%i\n", part1);
    printf("%i\n", part2);

    free(buf);
}

int fall(brick_t bricks[], int bricks_num) {
    int result = 0;
    for (int i = 0; i < bricks_num; i++) {
        int fallen = 0;
        for (;;) {
            bricks[i].corners[0].z--;
            bricks[i].corners[1].z--;
            if (bricks[i].corners[0].z <= 0 || bricks[i].corners[1].z <= 0) {
                break;
            }
            int collision = 0;
            for (int j = 0; j < bricks_num; j++) {
                if (i == j) continue;
                if (intersect(bricks[i], bricks[j])) {
                    collision = 1;
                    break;
                }
            }
            if (collision) {
                break;
            }
            bricks[i].fallen = 1;
            fallen = 1;
        }
        bricks[i].corners[0].z++;
        bricks[i].corners[1].z++;
        result += fallen;
    }
    
    return result;
}

int intersect(brick_t brick_a, brick_t brick_b) {
    if (
        (in_range(brick_b.corners[0].x, brick_a.corners[0].x, brick_a.corners[1].x) || in_range(brick_b.corners[1].x, brick_a.corners[0].x, brick_a.corners[1].x) || in_range(brick_a.corners[1].x, brick_b.corners[0].x, brick_b.corners[1].x) || in_range(brick_a.corners[0].x, brick_b.corners[0].x, brick_b.corners[1].x)) &&
        (in_range(brick_b.corners[0].y, brick_a.corners[0].y, brick_a.corners[1].y) || in_range(brick_b.corners[1].y, brick_a.corners[0].y, brick_a.corners[1].y) || in_range(brick_a.corners[1].y, brick_b.corners[0].y, brick_b.corners[1].y) || in_range(brick_a.corners[0].y, brick_b.corners[0].y, brick_b.corners[1].y)) &&
        (in_range(brick_b.corners[0].z, brick_a.corners[0].z, brick_a.corners[1].z) || in_range(brick_b.corners[1].z, brick_a.corners[0].z, brick_a.corners[1].z) || in_range(brick_a.corners[1].z, brick_b.corners[0].z, brick_b.corners[1].z) || in_range(brick_a.corners[0].z, brick_b.corners[0].z, brick_b.corners[1].z))
    ) {
        return 1;
    }

    return 0;
}