adventofcode2024/day12/c/day12.c

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

#define MAX_DIMENSION 1024
#define MAX_REGION 1024

void fill(char **map, int x, int y, int **region, int rows, int columns);

int main() {
    char c;

    char **map = calloc(MAX_DIMENSION, sizeof(map[0]));
    int rows = 0, columns, i = 0;
    map[rows] = calloc(MAX_DIMENSION, sizeof(map[0][0]));

    while ((c = getchar()) != EOF) {
        map[rows][i] = c;
        i++;
        if (c != '\n') {
            continue;
        }

        columns = i - 1;
        i = 0;
        rows++;
        map[rows] = calloc(MAX_DIMENSION, sizeof(map[0][0]));
    }

    int **visited = calloc(rows, sizeof(visited[0]));
    for (i = 0; i < rows; i++) {
        visited[i] = calloc(columns, sizeof(visited[0][0]));
    }
    int ***regions = calloc(MAX_REGION, sizeof(regions[0]));
    int region_count = 0;

    int cost = 0;
    int cost2 = 0;
    for (i = 0; i < rows; i++) {
        for (int j = 0; j < columns; j++) {
            if (visited[i][j]) {
                continue;
            }
            // Create new region
            regions[region_count] = calloc(rows, sizeof(regions[0][0]));
            for (int k = 0; k < rows; k++) {
                regions[region_count][k] = calloc(columns, sizeof(regions[0][0][0]));
            }

            // Fill new region
            fill(map, i, j, regions[region_count], rows, columns);

            int area = 0;
            // Copy to visited
            for (int k = 0; k < rows; k++) {
                for (int l = 0; l < columns; l++) {
                    visited[k][l] |= regions[region_count][k][l];
                    area += regions[region_count][k][l];
                }
            }
            // Calculate perimeter
            int perimeter = 0;
            for (int k = 0; k < rows; k++) {
                for (int l = 0; l < columns; l++) {
                    if (!regions[region_count][k][l]) {
                        continue;
                    }
                    int row;
                    int column;
                    // Up
                    row = k - 1;
                    column = l;
                    if (row < 0 || !regions[region_count][row][column]) {
                        perimeter += 1;
                    }
                    // Down
                    row = k + 1;
                    column = l;
                    if (row >= rows || !regions[region_count][row][column]) {
                        perimeter += 1;
                    }
                    // Left
                    row = k;
                    column = l + 1;
                    if (column >= columns || !regions[region_count][row][column]) {
                        perimeter += 1;
                    }
                    // Right
                    row = k;
                    column = l - 1;
                    if (column < 0 || !regions[region_count][row][column]) {
                        perimeter += 1;
                    }
                }
            }

            cost += area * perimeter;

            // Calculate perimeter task two
            perimeter = 0;
            for (int k = 0; k < rows; k++) {
                for (int l = 0; l < columns; l++) {
                    if (!regions[region_count][k][l]) {
                        continue;
                    }

                    if (k == 0) {
                        if (l == 0 || !regions[region_count][k][l-1]) {
                            perimeter++;
                        }
                    } else if (!regions[region_count][k-1][l]) {
                        if (l == 0 || !regions[region_count][k][l-1] || (regions[region_count][k][l-1] && regions[region_count][k][l-1] == regions[region_count][k-1][l-1])) {
                            perimeter++;
                        }
                    }

                    if (k == rows - 1) {
                        if (l == 0 || !regions[region_count][k][l-1]) {
                            perimeter++;
                        }
                    } else if (!regions[region_count][k+1][l]) {
                        if (l == 0 || !regions[region_count][k][l-1] || (regions[region_count][k][l-1] && regions[region_count][k][l-1] == regions[region_count][k+1][l-1])) {
                            perimeter++;
                        }
                    }


                    if (l == 0) {
                        if (k == 0 || !regions[region_count][k-1][l]) {
                            perimeter++;
                        }
                    } else if (!regions[region_count][k][l-1]) {
                        if (k == 0 || !regions[region_count][k-1][l] || (regions[region_count][k-1][l] && regions[region_count][k-1][l] == regions[region_count][k-1][l-1])) {
                            perimeter++;
                        }
                    }

                    if (l == columns - 1) {
                        if (k == 0 || !regions[region_count][k-1][l]) {
                            perimeter++;
                        }
                    } else if (!regions[region_count][k][l+1]) {
                        if (k == 0 || !regions[region_count][k-1][l] || (regions[region_count][k-1][l] && regions[region_count][k-1][l] == regions[region_count][k-1][l+1])) {
                            perimeter++;
                        }
                    }
                }
            }
            cost2 += area * perimeter;

            region_count++;
        }
    }

    printf("%i\n", cost);
    printf("%i\n", cost2);

    for (i = 0; i < region_count; i++) {
        for (int j = 0; j < rows; j++) {
            free(regions[i][j]);
        }
        free(regions[i]);
    }
    free(regions);
    for (i = 0; i < rows; i++) {
        free(visited[i]);
    }
    free(visited);
    for (i = 0; i < rows + 1; i++) {
        free(map[i]);
    }
    free(map);
}

void fill(char **map, int x, int y, int **region, int rows, int columns) {
    region[x][y] = 1;

    int row;
    int column;
    // Up
    row = x - 1;
    column = y;
    if (row >= 0 && map[row][column] == map[x][y] && !region[row][column]) {
        fill(map, row, column, region, rows, columns);
    }
    // Down
    row = x + 1;
    column = y;
    if (row < rows && map[row][column] == map[x][y] && !region[row][column]) {
        fill(map, row, column, region, rows, columns);
    }
    // Left
    row = x;
    column = y + 1;
    if (column < columns && map[row][column] == map[x][y] && !region[row][column]) {
        fill(map, row, column, region, rows, columns);
    }
    // Right
    row = x;
    column = y - 1;
    if (column >= 0 && map[row][column] == map[x][y] && !region[row][column]) {
        fill(map, row, column, region, rows, columns);
    }
}