adventofcode2023/day14/c/day14.c

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

#define LINE_MAX_LENGTH 256
#define MAX_ROUNDED_ROCKS 8*1024
#define MAX_HISTORY_SIZE 2048
#define abs(a) ((a) > 0 ? (a) : -(a))
#define CYCLES 1000000000

typedef enum tile {
    EMPTY,
    ROUNDED_ROCK,
    CUBE_ROCK,
} tile_t;

typedef struct position {
    int x;
    int y;
} position_t;

void tilt(tile_t map[LINE_MAX_LENGTH][LINE_MAX_LENGTH], int x, int y, int dir[2]);

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

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

    position_t rocks[MAX_ROUNDED_ROCKS];
    int rocks_num = 0, x = 0, y = 0;

    tile_t map[LINE_MAX_LENGTH][LINE_MAX_LENGTH];

    while ((c = getchar()) != EOF) {
        *p++ = c;
        if (c == '\n') {
            x = 0;
            p = buf;
            while (*p != '\n') {
                switch (*p) {
                    case '.':
                        map[x][y] = EMPTY;
                        break;
                    case '#':
                        map[x][y] = CUBE_ROCK;
                        break;
                    case 'O':
                        map[x][y] = ROUNDED_ROCK;
                        rocks[rocks_num].x = x;
                        rocks[rocks_num].y = y;
                        rocks_num++;
                        break;
                }
                p++;
                x++;
            }

            y++;
            memset(buf, 0, LINE_MAX_LENGTH);
            p = buf;
        }
    }

    int dir[2] = {0, -1};
    tilt(map, x, y, dir);


    int part1 = 0;
    for (int i = 0; i < y; i++) {
        for (int j = 0; j < x; j++) {
            if (map[j][i] == ROUNDED_ROCK) {
                part1 += y - i;
            }
        }
    }

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

    tile_t ***history = (tile_t***)malloc(MAX_HISTORY_SIZE * sizeof(tile_t**));
    for (int i = 0; i < MAX_HISTORY_SIZE; i++) {
        history[i] = malloc(LINE_MAX_LENGTH * LINE_MAX_LENGTH * sizeof(tile_t));
    }
    int history_num = 0;

    int offset = 0, period = 0;
    for (int i = 0; i < CYCLES; i++) {
        int found = 0;
        for (int j = 0; j < history_num; j++) {
            if (!memcmp(map, history[j], LINE_MAX_LENGTH * LINE_MAX_LENGTH * sizeof(tile_t))) {
                offset = j;
                period = history_num - j;
                found = 1;
                break;
            }
        }
        if (!found) {
            memcpy(history[history_num], map, LINE_MAX_LENGTH * LINE_MAX_LENGTH * sizeof(tile_t));
            history_num++;
        }
        if (found) {
            break;
        }
        if (i != 0) {
            dir[0] = 0;
            dir[1] = -1;
            tilt(map, x, y, dir);
        }
        dir[0] = -1;
        dir[1] = 0;
        tilt(map, x, y, dir);
        dir[0] = 0;
        dir[1] = 1;
        tilt(map, x, y, dir);
        dir[0] = 1;
        dir[1] = 0;
        tilt(map, x, y, dir);
    }

    for (int i = 0; i < (CYCLES - history_num) % period; i++) {
        dir[0] = 0;
        dir[1] = -1;
        tilt(map, x, y, dir);
        dir[0] = -1;
        dir[1] = 0;
        tilt(map, x, y, dir);
        dir[0] = 0;
        dir[1] = 1;
        tilt(map, x, y, dir);
        dir[0] = 1;
        dir[1] = 0;
        tilt(map, x, y, dir);
    }

    int part2 = 0;
    for (int i = 0; i < y; i++) {
        for (int j = 0; j < x; j++) {
            if (map[j][i] == ROUNDED_ROCK) {
                part2 += y - i;
            }
        }
    }

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

    for (int i = 0; i < MAX_HISTORY_SIZE; i++) {
        free(history[i]);
    }
    free(history);
    free(buf);
}

void tilt(tile_t map[LINE_MAX_LENGTH][LINE_MAX_LENGTH], int x, int y, int dir[2]) {
    position_t start;
    int *iterate, iter_length;
    if (dir[0] == 1) {
        start.x = x - 1;
        start.y = 0;
        iterate = &start.y;
        iter_length = y;
    } else if (dir[0] == -1) {
        start.x = 0;
        start.y = 0;
        iterate = &start.y;
        iter_length = y;
    } else if (dir[1] == 1) {
        start.x = 0;
        start.y = y - 1;
        iterate = &start.x;
        iter_length = x;
    } else if (dir[1] == -1) {
        start.x = 0;
        start.y = 0;
        iterate = &start.x;
        iter_length = x;
    }

    position_t to_put;
    for (int i = 0; i < iter_length; i++) {
        *iterate = i;
        memcpy(&to_put, &start, sizeof(position_t));
        int *iterate_secondary = iter_length == x ? &to_put.y : &to_put.x, iter_length_secondary = iter_length == x ? y : x;
        for (int j = 0; j < iter_length_secondary; j++) {
            int cx = start.x - dir[0] * j;
            int cy = start.y - dir[1] * j;
            tile_t current_tile = map[cx][cy];
            switch (current_tile) {
                case EMPTY:
                    break;
                case ROUNDED_ROCK:
                    map[cx][cy] = EMPTY;
                    map[to_put.x][to_put.y] = ROUNDED_ROCK;
                    to_put.x -= dir[0];
                    to_put.y -= dir[1];
                    break;
                case CUBE_ROCK:
                    to_put.x = cx - dir[0];
                    to_put.y = cy - dir[1];
                    break;
            }
        }
    }
}