Day10

day10/c/day10.c

@@ -0,0 +1,102 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX_DIMENSION 128
+
+int get_trails(char**, int, int, int, int, int**);
+
+int main() {
+    char c;
+
+    char **map = calloc(MAX_DIMENSION, sizeof(map[0]));
+
+    int rows = 0, i = 0, columns;
+    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;
+        rows++;
+        i = 0;
+        map[rows] = calloc(MAX_DIMENSION, sizeof(map[0][0]));
+    }
+
+    int **reachable = calloc(rows, sizeof(reachable[0]));
+    for (i = 0; i < rows; i++) {
+        reachable[i] = calloc(columns, sizeof(reachable[0][0]));
+    }
+
+    int score = 0;
+    int rating = 0;
+    // For each '0'
+    for (i = 0; i < rows; i++) {
+        for (int j = 0; j < columns; j++) {
+            if (map[i][j] != '0') {
+                continue;
+            }
+
+            rating += get_trails(map, rows, columns, i, j, reachable);
+            // Count reachable
+            for (int k = 0; k < rows; k++) {
+                for (int l = 0; l < columns; l++) {
+                    score += reachable[k][l];
+                    reachable[k][l] = 0;
+                }
+            }
+        }
+    }
+
+    for (i = 0; i < rows; i++) {
+        free(reachable[i]);
+    }
+    free(reachable);
+    for (i = 0; i < rows + 1; i++) {
+        free(map[i]);
+    }
+    free(map);
+
+    printf("%i\n", score);
+    printf("%i\n", rating);
+}
+
+int get_trails(char** map, int rows, int columns, int row, int column, int** reachable) {
+    if (map[row][column] == '9') {
+        reachable[row][column] = 1;
+        return 1;
+    }
+
+    int x, y;
+    char next = map[row][column] + 1;
+    int trails = 0;
+    // up
+    x = row - 1;
+    y = column;
+    if (x >= 0 && map[x][y] == next) {
+        trails += get_trails(map, rows, columns, x, y, reachable);
+    }
+    // down
+    x = row + 1;
+    y = column;
+    if (x < rows && map[x][y] == next) {
+        trails += get_trails(map, rows, columns, x, y, reachable);
+    }
+    // left
+    x = row;
+    y = column + 1;
+    if (y < columns && map[x][y] == next) {
+        trails += get_trails(map, rows, columns, x, y, reachable);
+    }
+    // right
+    x = row;
+    y = column - 1;
+    if (y >= 0 && map[x][y] == next) {
+        trails += get_trails(map, rows, columns, x, y, reachable);
+    }
+
+    return trails;
+}