16/2024

Author: breadadams

2024/16/example.txt

@@ -0,0 +1,17 @@
+#################
+#...#...#...#..E#
+#.#.#.#.#.#.#.#.#
+#.#.#.#...#...#.#
+#.#.#.#.###.#.#.#
+#...#.#.#.....#.#
+#.#.#.#.#.#####.#
+#.#...#.#.#.....#
+#.#.#####.#.###.#
+#.#.#.......#...#
+#.#.###.#####.###
+#.#.#...#.....#.#
+#.#.#.#####.###.#
+#.#.#.........#.#
+#.#.#.#########.#
+#S#.............#
+#################

2024/16/index.test.ts

@@ -0,0 +1,25 @@
+import { expect, describe, test } from "bun:test";
+import { part1, part2 } from ".";
+import { getInputs } from "../../utils/get-inputs";
+
+const { exampleInput, puzzleInput } = await getInputs("2024/16");
+
+describe("part 1", () => {
+  test("example", () => {
+    expect(part1(exampleInput)).toBe(11048);
+  });
+
+  test("puzzle", () => {
+    expect(part1(puzzleInput)).toBe(92432);
+  });
+});
+
+describe("part 2", () => {
+  test("example", () => {
+    expect(part2(exampleInput)).toBe(64);
+  });
+
+  test("puzzle", () => {
+    expect(part2(puzzleInput)).toBe(458);
+  });
+});

2024/16/index.ts

@@ -0,0 +1,218 @@
+import { timePart1, timePart2 } from "../../utils/time-part";
+
+const parseInput = (input: string) => {
+  return input.split("\n").map((row) => row.split(""));
+};
+
+type InputMap = ReturnType<typeof parseInput>;
+
+const findCell = (char: string, map: InputMap) => {
+  const y = map.findIndex((row) => row.includes(char));
+  const x = map[y].indexOf(char);
+
+  return { x, y };
+};
+
+const getStartingPosition = (map: InputMap) => findCell("S", map);
+const getEndPosition = (map: InputMap) => findCell("E", map);
+
+const DIRECTIONS = ["N", "E", "S", "W"] as const;
+type Direction = (typeof DIRECTIONS)[number];
+
+type Coordinate = { x: number; y: number };
+
+const positionToKey = (position: Coordinate, direction?: Direction) => {
+  const positionKey = `${position.x},${position.y}`;
+
+  if (direction) {
+    return `${positionKey}:${direction}`;
+  }
+
+  return positionKey;
+};
+
+const rotate = (
+  direction: Direction,
+  { clockwise } = { clockwise: true }
+): Direction => {
+  if (direction === "N" && !clockwise) {
+    return "W";
+  }
+
+  return DIRECTIONS[
+    (DIRECTIONS.indexOf(direction) + (clockwise ? 1 : -1)) % DIRECTIONS.length
+  ];
+};
+
+const MOVEMENTS = {
+  N: { x: 0, y: -1 },
+  E: { x: 1, y: 0 },
+  S: { x: 0, y: 1 },
+  W: { x: -1, y: 0 },
+} satisfies Record<Direction, Coordinate>;
+
+const move = (position: Coordinate, direction: Direction) => {
+  const movement = MOVEMENTS[direction];
+
+  return { x: position.x + movement.x, y: position.y + movement.y };
+};
+
+const readCell = ({ x, y }: Coordinate, map: InputMap) => map[y]?.[x];
+
+type QueueEntry = {
+  direction: Direction;
+  position: Coordinate;
+  score: number;
+  visited: Coordinate[];
+};
+
+const getBestScore = (map: InputMap) => {
+  const start = getStartingPosition(map);
+  const end = getEndPosition(map);
+
+  const queue: QueueEntry[] = [
+    {
+      direction: "E",
+      position: start,
+      score: 0,
+      visited: [start],
+    },
+  ];
+
+  const globalVisited = new Set<string>();
+  let bestScore: number | null = null;
+
+  while (queue.length) {
+    queue.sort((a, b) => a.score - b.score);
+
+    const route = queue.shift()!;
+    const baseKey = positionToKey(route.position, route.direction);
+
+    if (globalVisited.has(baseKey)) {
+      continue;
+    }
+    globalVisited.add(baseKey);
+
+    if (route.position.x === end.x && route.position.y === end.y) {
+      if (typeof bestScore !== "number" || route.score < bestScore) {
+        bestScore = route.score;
+      }
+
+      continue;
+    }
+
+    const movedForward = move(route.position, route.direction);
+    const cell = readCell(movedForward, map);
+
+    if (cell !== "#") {
+      queue.push({
+        ...route,
+        position: movedForward,
+        score: route.score + 1,
+        visited: [...route.visited, movedForward],
+      });
+    }
+
+    queue.push({
+      ...route,
+      direction: rotate(route.direction),
+      score: route.score + 1000,
+      visited: [...route.visited],
+    });
+
+    queue.push({
+      ...route,
+      direction: rotate(route.direction, { clockwise: false }),
+      score: route.score + 1000,
+      visited: [...route.visited],
+    });
+  }
+
+  return bestScore ?? 0;
+};
+
+export const part1 = timePart1((input: string) => {
+  const map = parseInput(input);
+  const bestScore = getBestScore(map);
+
+  return bestScore;
+});
+
+export const part2 = timePart2((input: string) => {
+  const map = parseInput(input);
+  const bestScore = getBestScore(map);
+  const startingPosition = getStartingPosition(map);
+  const endPosition = getEndPosition(map);
+
+  const queue: QueueEntry[] = [
+    {
+      visited: [startingPosition],
+      position: startingPosition,
+      direction: "E",
+      score: 0,
+    },
+  ];
+
+  const globalVisited = new Map<string, number>();
+  const pathsToEnd: QueueEntry["visited"][] = [];
+
+  while (queue.length) {
+    const route = queue.shift()!;
+    const baseKey = positionToKey(route.position, route.direction);
+
+    if (
+      route.score > bestScore ||
+      (globalVisited.has(baseKey) && globalVisited.get(baseKey)! < route.score)
+    ) {
+      continue;
+    }
+
+    globalVisited.set(baseKey, route.score);
+
+    if (
+      route.position.x === endPosition.x &&
+      route.position.y === endPosition.y &&
+      route.score === bestScore
+    ) {
+      pathsToEnd.push(route.visited);
+      continue;
+    }
+
+    const movedForward = move(route.position, route.direction);
+    const cell = readCell(movedForward, map);
+
+    if (cell !== "#") {
+      queue.push({
+        ...route,
+        position: movedForward,
+        score: route.score + 1,
+        visited: [...route.visited, movedForward],
+      });
+    }
+
+    queue.push({
+      ...route,
+      direction: rotate(route.direction),
+      score: route.score + 1000,
+      visited: [...route.visited],
+    });
+
+    queue.push({
+      ...route,
+      direction: rotate(route.direction, { clockwise: false }),
+      score: route.score + 1000,
+      visited: [...route.visited],
+    });
+  }
+
+  const bestSeats = new Set<string>();
+
+  for (const pathToGoal of pathsToEnd) {
+    for (const position of pathToGoal) {
+      const key = positionToKey(position);
+      bestSeats.add(key);
+    }
+  }
+
+  return bestSeats.size;
+});

README.md

@@ -6,6 +6,7 @@
 
 |                    Day                     | Part 1 | Part 2 |
 | :----------------------------------------: | :----: | :----: |
+| [16](https://adventofcode.com/2024/day/16) |   ✅   |   ✅   |
 | [15](https://adventofcode.com/2024/day/15) |   ✅   |   ✅   |
 | [14](https://adventofcode.com/2024/day/14) |   ✅   |   ✅   |
 | [13](https://adventofcode.com/2024/day/13) |   ✅   |   ✅   |