Day20

day20/c/day20.c

@@ -0,0 +1,220 @@
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+#define MAX_DIMENSION 1024
+#define QUEUE_MAX 32*1024
+#define abs(a) ((a) < 0 ? (-(a)) : (a))
+
+const int directions[][2] = {
+    {0, 1},
+    {1, 0},
+    {0, -1},
+    {-1, 0}
+};
+
+#define directions_len (sizeof(directions)/sizeof(directions[0]))
+
+typedef enum tile {
+    EMPTY,
+    WALL,
+} tile_t;
+
+int ospf(tile_t **map, int rows, int colums, int start[2], int end[2]);
+
+int main() {
+    char c;
+
+    tile_t **map = calloc(MAX_DIMENSION, sizeof(map[0]));
+    int rows = 0, columns, i = 0;
+    map[0] = calloc(MAX_DIMENSION, sizeof(map[0][0]));
+
+    int start[2], end[2];
+    while ((c = getchar()) != EOF) {
+        switch(c) {
+            case '#':
+                map[rows][i] = WALL;
+                break;
+            case '.':
+                map[rows][i] = EMPTY;
+                break;
+            case 'S':
+                map[rows][i] = EMPTY;
+                start[0] = rows;
+                start[1] = i;
+                break;
+            case 'E':
+                map[rows][i] = EMPTY;
+                end[0] = rows;
+                end[1] = i;
+                break;
+        }
+
+        i++;
+        if (c != '\n') {
+            continue;
+        }
+
+        columns = i - 1;
+        i = 0;
+        rows++;
+        map[rows] = calloc(MAX_DIMENSION, sizeof(map[0][0]));
+    }
+
+    int without_cheats = 0;
+
+    // Shortest path search
+    uint32_t **costs = calloc(rows, sizeof(costs[0]));
+    for (int i = 0; i < rows; i++) {
+        costs[i] = calloc(columns, sizeof(costs[0][0]));
+        memset(costs[i], 255, columns * sizeof(costs[0][0]));
+    }
+
+    int (*queue)[2] = calloc(QUEUE_MAX, sizeof(queue[0]));
+    int queue_num = 1;
+    // Start at 0,0
+    queue[0][0] = start[0];
+    queue[0][1] = start[1];
+    costs[start[0]][start[1]] = 0;
+
+    while (queue_num > 0) {
+        // Pop first
+        int x = queue[0][0];
+        int y = queue[0][1];
+        uint32_t cost = costs[x][y];
+
+        if (x == end[0] && y == end[1]) {
+            without_cheats = cost;
+            break;
+        }
+
+        for (int i = 0; i < queue_num - 1; i++) {
+            queue[i][0] = queue[i+1][0];
+            queue[i][1] = queue[i+1][1];
+        }
+        queue_num--;
+
+        // Check each direction
+        for (int i = 0; i < directions_len; i++) {
+            int dx = directions[i][0];
+            int dy = directions[i][1];
+
+            int next_x = x + dx;
+            int next_y = y + dy;
+
+            // Outside of map, into wall, or better path exists
+            if (next_x < 0 || next_y < 0 || next_x >= rows || next_y >= columns || map[next_x][next_y] || costs[next_x][next_y] <= cost + 1) {
+                continue;
+            }
+
+            // Insert into queue
+            uint32_t next_cost = cost + 1;
+            costs[next_x][next_y] = next_cost;
+            int insert_idx;
+            for (insert_idx = 0; insert_idx < queue_num; insert_idx++) {
+                int qx = queue[insert_idx][0];
+                int qy = queue[insert_idx][1];
+                if (costs[qx][qy] > next_cost) {
+                    break;
+                }
+            }
+
+            for (int j = queue_num; j > insert_idx; j--) {
+                queue[j][0] = queue[j-1][0];
+                queue[j][1] = queue[j-1][1];
+            }
+            queue[insert_idx][0] = next_x;
+            queue[insert_idx][1] = next_y;
+            queue_num++;
+        }
+    }
+
+    int good_cheats = 0;
+    int good_cheat_limit = 100;
+
+    // Find where to cheat
+    for (i = 0; i < rows; i++) {
+        for (int j = 0; j < columns; j++) {
+            if (map[i][j] != EMPTY) {
+                continue;
+            }
+            // Try each direction and check if there's a wall
+            for (int k = 0; k < directions_len; k++) {
+                int dx = directions[k][0];
+                int dy = directions[k][1];
+                int x = i + dx;
+                int y = j + dy;
+
+                if (x < 0 || y < 0 || x >= rows || y >= columns || map[x][y] != WALL) {
+                    continue;
+                }
+
+                // Now check whether we can get back to the track to shorten out time
+                for (int l = 0; l < directions_len; l++) {
+                    int dx = directions[l][0];
+                    int dy = directions[l][1];
+                    int xx = x + dx;
+                    int yy = y + dy;
+
+                    if (xx < 0 || yy < 0 || xx >= rows || yy >= columns || map[xx][yy] == WALL) {
+                        continue;
+                    }
+
+                    // Not good cheat enough
+                    if (costs[xx][yy] < costs[i][j] + good_cheat_limit + 2) {
+                        continue;
+                    }
+
+                    good_cheats++;
+                }
+            }
+        }
+    }
+
+    int good_cheats2 = 0;
+    int good_cheat_limit2 = 100;
+
+    // Find where to cheat
+    for (i = 0; i < rows; i++) {
+        for (int j = 0; j < columns; j++) {
+            if (map[i][j] != EMPTY) {
+                continue;
+            }
+
+            // Check submap, we can get to anywhere inside a 20 radius "circle" by activating the cheat here
+            for (int k = i-20; k <= i+20; k++) {
+                for (int l = j-(20-abs(k-i)); l <= j+(20-abs(k-i)); l++) {
+                    if (k < 0 || l < 0 || k >= rows || l >= columns) {
+                        continue;
+                    }
+
+                    // We don't want to get into a wall
+                    if (map[k][l] == WALL) {
+                        continue;
+                    }
+
+                    // Not good cheat enough
+                    if (costs[k][l] < costs[i][j] + good_cheat_limit2 + abs(k-i) + abs(l-j)) {
+                        continue;
+                    }
+
+                    good_cheats2++;
+                }
+            }
+        }
+    }
+
+    printf("%i\n", good_cheats);
+    printf("%i\n", good_cheats2);
+
+    for (i = 0; i < rows; i++) {
+        free(costs[i]);
+    }
+    free(costs);
+    for (i = 0; i < rows + 1; i++) {
+        free(map[i]);
+    }
+    free(map);
+}

day20/input.txt

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