2018/Day17/Day17A.c

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

#define AT(x, y) grid[(y) * x_max + (x)]

void get_limits(FILE *file, int *x_min, int *x_max, int *y_min, int *y_max) {
    char *line = NULL;
    size_t len;

    *x_min = INT_MAX;
    *x_max = INT_MAX;
    *x_max = 0;
    *y_max = 0;

    while (getline(&line, &len, file) != -1) {
        int xa, xb, ya, yb;
        if (sscanf(line, "x=%d, y=%d..%d", &xa, &ya, &yb) == 3) {
            if (xa < *x_min) *x_min = xa;
            if (xa + 1 > *x_max) *x_max = xa + 1;
            if (ya < *y_min) *y_min = ya;
            if (yb + 1 > *y_max) *y_max = yb + 1;
        } else if (sscanf(line, "y=%d, x=%d..%d", &ya, &xa, &xb) == 3) {
            if (xa < *x_min) *x_min = xa;
            if (xb + 1 > *x_max) *x_max = xa + 1;
            if (ya < *y_min) *y_min = ya;
            if (ya + 1 > *y_max) *y_max = yb + 1;
        } else {
            break;
        }
    }

    *x_max += 10;
        *x_min -= 10;
    printf("grid: x=%d..%d y=%d..%d\n", *x_min, *x_max, *y_min, *y_max);

    rewind(file);
}

void build_grid(FILE *file, char *grid, int x_max) {
    char *line = NULL;
    size_t len;
    while (getline(&line, &len, file) != -1) {
        int xa, xb, ya, yb;
        if (sscanf(line, "x=%d, y=%d..%d", &xa, &ya, &yb) == 3) {
            printf("x=%d, y=%d..%d\n", xa, ya, yb);
            for (int y = ya; y <= yb; y++)
                AT(xa, y) = '#';
        } else if (sscanf(line, "y=%d, x=%d..%d", &ya, &xa, &xb) == 3) {
            printf("x=%d..%d, y=%d\n", xa, xb, ya);
            for (int x = xa; x <= xb; x++)
                AT(x, ya) = '#';
        } else {
            break;
        }
    }
    grid[500] = '+';
}

void print_grid(char *grid, int x_min, int x_max, int y_min, int y_max) {
    printf("\n");
    printf("      "); for (int x = x_min; x < x_max; x++) printf("%d", x / 100 % 10);  printf("\n");
    printf("      "); for (int x = x_min; x < x_max; x++) printf("%d", x / 10 % 10);   printf("\n");
    printf("      "); for (int x = x_min; x < x_max; x++) printf("%d", x % 10);        printf("\n");

    for (int y = 0; y < y_max + 3; y++) {
        if (y < y_min || y >= y_max)
            printf("\033[41m");
        printf("%4d  \033[0m", y);
        for (int x = x_min; x < x_max; x++) {
            switch (grid[y * x_max + x]) {
            case '.':
                putchar(' ');
                putchar(' ');
                break;

            case '|':
                printf("\033[44m\u2551\u2551\033[0m");
                break;

            case '~':
                printf("\033[44m\u2248\u2248\033[0m");
                break;

            case '#':
                printf("\033[33m\u2588\u2588\033[0m");
                break;

            case '+':
                printf("\033[41m\u256C\u256C\033[0m");
                break;

            default:
                assert(0);
            }
        }
        putchar('\n');
    }
}

char *read_grid(FILE *file, int *x_min, int *x_max, int *y_min, int *y_max) {
    get_limits(file, x_min, x_max, y_min, y_max);

    size_t size = (*y_max + 50) * *x_max;
    char *grid = malloc(size);
    memset(grid, '.', size);

    build_grid(file, grid, *x_max);
    return grid;
}


void step(char *grid, int x_min, int x_max, int y_min, int y_max) {
    for (int y = 0; y < y_max + 50; y++) {
        for (int x = x_min; x < x_max; x++) {
            if (AT(x, y) == '+' || AT(x, y) == '|') {
                if (AT(x, y + 1) == '.') {
                    AT(x, y + 1) = '|';
                } else if (AT(x, y + 1) == '#' || AT(x, y + 1) == '~') {
                    int is_still = 1;
                    int left_wall = -1, right_wall = -1;

                    for (int x_ = x; x_ >= x_min - 1; x_--) {
                        if (AT(x_, y) == '#') {
                            left_wall = x_ + 1;
                            break;
                        } else if (AT(x_, y + 1) == '.' || AT(x_, y + 1) == '|') {
                            is_still = 0;
                            left_wall = x_;
                            break;
                        }
                    }

                    for (int x_ = x; x_ <= x_max; x_++) {
                        if (AT(x_, y) == '#') {
                            right_wall = x_ - 1;
                            break;
                        } else if (AT(x_, y + 1) == '.' || AT(x_, y + 1) == '|') {
                            is_still = 0;
                            right_wall = x_;
                            break;
                        }
                    }

                    if (left_wall != -1 && right_wall != -1) {
                        for (int x_ = left_wall; x_ <= right_wall; x_++) {
                            assert(AT(x_, y) != '#');
                            AT(x_, y) = is_still ? '~' : '|';
                        }
                    }
                }
            }
        }
    }
}

int count_water(char *grid, int x_min, int x_max, int y_min, int y_max) {
    int water = 0;
    for (int y = y_min; y < y_max; y++) {
        for (int x = x_min; x < x_max; x++) {
            water += (AT(x, y) == '~') ? 1 : 0;
        }
    }
    return water;
}

int main(int argc, char **argv) {
    if (argc != 2) {
        printf("Usage: %s [input]\n", argv[0]);
        return EXIT_FAILURE;
    }
    FILE *file = fopen(argv[1], "r");

    int x_min, x_max, y_min, y_max;
    char *grid = read_grid(file, &x_min, &x_max, &y_min, &y_max);

    print_grid(grid, x_min, x_max, y_min, y_max);
    int last_water = -1, water = -1;
    int extra_steps = 0;
    do {
        step(grid, x_min, x_max, y_min, y_max);

        last_water = water;
        water = count_water(grid, x_min, x_max, y_min, y_max);
        printf("Water: %d\r", water);

        if (last_water == water)
            extra_steps += 1;
        else
            extra_steps = 0;
    } while (extra_steps < 200);

    print_grid(grid, x_min, x_max, y_min, y_max);
    printf("Water: %d\n", water);
}