before optimizations

src/2024/day16.js

@@ -0,0 +1,62 @@
+const opposite = { up: "down", down: "up", left: "right", right: "left" };
+
+function solve(input, part2 = false) {
+  let map = input.split("\n").map(line => line.split(""));
+  let sy = map.findIndex(line => line.includes("S"));
+  let sx = map[sy].indexOf("S");
+  let ey = map.findIndex(line => line.includes("E"));
+  let ex = map[ey].indexOf("E");
+  let current = { x: sx, y: sy, score: 0, dir: "right", path: ["0,0"] };
+  let queue = [current];
+  let visited = new Map();
+  let min = Infinity;
+  let paths = [];
+  visited.set(`${current.x},${current.y}`, 0);
+  while (queue.length > 0) {
+    current = queue.shift();
+    if (current.x === ex && current.y === ey) {
+      if (current.score < min) paths = [current.path];
+      if (current.score === min) paths.push(current.path);
+      min = Math.min(min, current.score);
+      continue;
+    }
+    let neighbors = [
+      { x: current.x - 1, y: current.y, dir: "left" },
+      { x: current.x + 1, y: current.y, dir: "right" },
+      { x: current.x, y: current.y - 1, dir: "up" },
+      { x: current.x, y: current.y + 1, dir: "down" },
+    ]
+      .filter(neighbor => neighbor.dir !== opposite[current.dir])
+      .filter(neighbor => map[neighbor.y]?.[neighbor.x] !== "#")
+      .map(neighbor => ({
+        ...neighbor,
+        path: current.path.concat(`${neighbor.x},${neighbor.y}`),
+        score: current.score + (neighbor.dir !== current.dir ? 1001 : 1),
+      }));
+    neighbors.forEach(neighbor => {
+      if (
+        !visited.has(`${neighbor.x},${neighbor.y},${neighbor.dir}`) ||
+        visited.get(`${neighbor.x},${neighbor.y},${neighbor.dir}`) >
+          neighbor.score
+      ) {
+        queue.push(neighbor);
+        visited.set(
+          `${neighbor.x},${neighbor.y},${neighbor.dir}`,
+          neighbor.score + (part2 ? 1 : 0),
+        );
+      }
+    });
+  }
+  return { min, paths };
+}
+
+export function part1(input) {
+  return solve(input).min;
+}
+
+export function part2(input) {
+  return solve(input, true).paths.reduce(
+    (acc, path) => acc.union(new Set(path)),
+    new Set(),
+  ).size;
+}

src/2024/day16.spec.js

@@ -0,0 +1,114 @@
+import { part1, part2 } from "./day16.js";
+import readInput from "../utils/read-input.js";
+
+const input = readInput(import.meta.url);
+
+describe("day16 2024", () => {
+  describe("part1", () => {
+    test("it should work for part 1 examples", () => {
+      expect(
+        part1(
+          [
+            "###############",
+            "#.......#....E#",
+            "#.#.###.#.###.#",
+            "#.....#.#...#.#",
+            "#.###.#####.#.#",
+            "#.#.#.......#.#",
+            "#.#.#####.###.#",
+            "#...........#.#",
+            "###.#.#####.#.#",
+            "#...#.....#.#.#",
+            "#.#.#.###.#.#.#",
+            "#.....#...#.#.#",
+            "#.###.#.#.#.#.#",
+            "#S..#.....#...#",
+            "###############",
+          ].join("\n"),
+        ),
+      ).toEqual(7036);
+
+      expect(
+        part1(
+          [
+            "#################",
+            "#...#...#...#..E#",
+            "#.#.#.#.#.#.#.#.#",
+            "#.#.#.#...#...#.#",
+            "#.#.#.#.###.#.#.#",
+            "#...#.#.#.....#.#",
+            "#.#.#.#.#.#####.#",
+            "#.#...#.#.#.....#",
+            "#.#.#####.#.###.#",
+            "#.#.#.......#...#",
+            "#.#.###.#####.###",
+            "#.#.#...#.....#.#",
+            "#.#.#.#####.###.#",
+            "#.#.#.........#.#",
+            "#.#.#.#########.#",
+            "#S#.............#",
+            "#################",
+          ].join("\n"),
+        ),
+      ).toEqual(11048);
+    });
+
+    test("it should work for part 1 input", () => {
+      expect(part1(input)).toEqual(106512);
+    });
+  });
+
+  describe("part2", () => {
+    test("it should work for part 2 examples", () => {
+      expect(
+        part2(
+          [
+            "###############",
+            "#.......#....E#",
+            "#.#.###.#.###.#",
+            "#.....#.#...#.#",
+            "#.###.#####.#.#",
+            "#.#.#.......#.#",
+            "#.#.#####.###.#",
+            "#...........#.#",
+            "###.#.#####.#.#",
+            "#...#.....#.#.#",
+            "#.#.#.###.#.#.#",
+            "#.....#...#.#.#",
+            "#.###.#.#.#.#.#",
+            "#S..#.....#...#",
+            "###############",
+          ].join("\n"),
+        ),
+      ).toEqual(45);
+
+      expect(
+        part2(
+          [
+            "#################",
+            "#...#...#...#..E#",
+            "#.#.#.#.#.#.#.#.#",
+            "#.#.#.#...#...#.#",
+            "#.#.#.#.###.#.#.#",
+            "#...#.#.#.....#.#",
+            "#.#.#.#.#.#####.#",
+            "#.#...#.#.#.....#",
+            "#.#.#####.#.###.#",
+            "#.#.#.......#...#",
+            "#.#.###.#####.###",
+            "#.#.#...#.....#.#",
+            "#.#.#.#####.###.#",
+            "#.#.#.........#.#",
+            "#.#.#.#########.#",
+            "#S#.............#",
+            "#################",
+          ].join("\n"),
+        ),
+      ).toEqual(64);
+    });
+
+    test("it should work for part 2 input", () => {
+      expect(part2(input)).toEqual(563);
+    });
+  });
+});