AoC18/day25p1/main.c

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

#include <glib.h>

struct coord4d {
    int x;
    int y;
    int z;
    int t;
};

struct point {
    struct coord4d c;
    GPtrArray *near;
};

struct point *parse_points(const char *fname, unsigned *len)
{
    FILE *f = fopen(fname, "r");
    if (!f) {
        perror(fname);
        return NULL;
    }

    GArray *array = g_array_new(FALSE, FALSE, sizeof(struct point));

    struct point point;
    while (fscanf(f, "%d,%d,%d,%d\n",
                &point.c.x, &point.c.y,
                &point.c.z, &point.c.t) == 4) {
        point.near = g_ptr_array_new();
        g_array_append_val(array, point);
    }

    *len = array->len;
    return (struct point *)g_array_free(array, FALSE);
}

void free_points(struct point *points, const unsigned len)
{
    for (struct point *point = points;
            point < points + len; point++) {
        g_ptr_array_free(point->near, TRUE);
    }
    g_free(points);
}

GHashTable *find_const(GPtrArray *consts, struct point *point)
{
    for (GHashTable **p = (GHashTable **)consts->pdata;
            p < (GHashTable **)consts->pdata + consts->len; p++) {
        if (g_hash_table_contains(*p, point)) return *p;
    }
    return NULL;
}

void merge_const(GPtrArray *consts, GHashTable *a, GHashTable *b)
{
    if (a == b) return;

    GHashTableIter iter;
    gpointer key, value;
    g_hash_table_iter_init(&iter, b);
    while (g_hash_table_iter_next(&iter, &key, &value)) {
        g_hash_table_add(a, key);
    }
    g_ptr_array_remove_fast(consts, b);
}

int main()
{
    unsigned points_len;
    struct point *points = parse_points("input", &points_len);
    if (!points) return 1;

    for (struct point *a = points;
            a < points + points_len; a++) {
        for (struct point *b = points;
                b < points + points_len; b++) {
            unsigned x = abs(a->c.x - b->c.x);
            unsigned y = abs(a->c.y - b->c.y);
            unsigned z = abs(a->c.z - b->c.z);
            unsigned t = abs(a->c.t - b->c.t);

            if (x + y + z + t <= 3) {
                g_ptr_array_add(a->near, b);
            }
        }
    }

    GPtrArray *consts = g_ptr_array_new();
    g_ptr_array_set_free_func(consts, (void (*)(void *))g_hash_table_destroy);

    for (struct point *p = points; p < points + points_len; p++) {
        GHashTable *constel = find_const(consts, p);
        if (!constel) {
            constel = g_hash_table_new(NULL, NULL);
            g_hash_table_add(constel, p);
            g_ptr_array_add(consts, constel);
        }

        for (struct point **p2 = (struct point **)p->near->pdata;
                p2 < (struct point **)p->near->pdata + p->near->len; p2++) {
            GHashTable *constel2 = find_const(consts, *p2);
            if (constel2) merge_const(consts, constel, constel2);

            g_hash_table_add(constel, *p2);
        }
    }

    printf("%u\n", consts->len);

    g_ptr_array_free(consts, TRUE);
    free_points(points, points_len);
    return 0;
}