04/2024

Author: breadadams

2024/04/index.ts

@@ -0,0 +1,180 @@
+import { getPuzzle } from "../../utils";
+
+const puzzleInput = getPuzzle(__dirname).trim();
+
+const wordsearch = puzzleInput.split("\n").map((row) => row.split(""));
+
+const WIDTH = wordsearch[0].length;
+const HEIGHT = wordsearch.length;
+
+const XMAS = "XMAS";
+
+type Entries<T> = { [K in keyof T]: [K, T[K]] }[keyof T][];
+
+type Coordinate = { x: number; y: number };
+
+const DIRECTION_MAP = {
+  N: { x: 0, y: -1 },
+  NE: { x: 1, y: -1 },
+  E: { x: 1, y: 0 },
+  SE: { x: 1, y: 1 },
+  S: { x: 0, y: 1 },
+  SW: { x: -1, y: 1 },
+  W: { x: -1, y: 0 },
+  NW: { x: -1, y: -1 },
+} as const satisfies Record<string, Coordinate>;
+
+const isOutOfBounds = (coord: Coordinate) => {
+  return coord.x < 0 || coord.x >= WIDTH || coord.y < 0 || coord.y >= HEIGHT;
+};
+
+// Part 1
+(() => {
+  console.time("part 1");
+  type QueueEntry = {
+    chars: string[];
+    direction: keyof typeof DIRECTION_MAP | undefined;
+    position: Coordinate;
+  };
+
+  let matches = 0;
+  const queue: QueueEntry[] = [];
+
+  for (let y = 0; y < HEIGHT; y++) {
+    for (let x = 0; x < WIDTH; x++) {
+      const char = wordsearch[y][x];
+
+      if (char === XMAS[0]) {
+        queue.push({
+          chars: [char],
+          direction: undefined,
+          position: { x, y },
+        });
+      }
+    }
+  }
+
+  while (queue.length > 0) {
+    const current = queue.shift();
+
+    if (current.chars.length === XMAS.length) {
+      matches += 1;
+      continue;
+    }
+
+    const nextChar = XMAS[current.chars.length];
+
+    if (typeof current.direction === "undefined") {
+      for (const element of Object.entries(DIRECTION_MAP) as Entries<
+        typeof DIRECTION_MAP
+      >) {
+        const [key, direction] = element;
+        const nextCell = {
+          x: current.position.x + direction.x,
+          y: current.position.y + direction.y,
+        };
+
+        if (isOutOfBounds(nextCell)) {
+          continue;
+        }
+
+        if (wordsearch[nextCell.y][nextCell.x] === nextChar) {
+          queue.push({
+            chars: [...current.chars, nextChar],
+            direction: key,
+            position: nextCell,
+          });
+        }
+      }
+    } else {
+      const direction = DIRECTION_MAP[current.direction];
+
+      const nextCell = {
+        x: current.position.x + direction.x,
+        y: current.position.y + direction.y,
+      };
+
+      if (isOutOfBounds(nextCell)) {
+        continue;
+      }
+
+      if (wordsearch[nextCell.y][nextCell.x] === nextChar) {
+        queue.push({
+          chars: [...current.chars, nextChar],
+          direction: current.direction,
+          position: nextCell,
+        });
+      }
+    }
+  }
+
+  console.log("part 1 matches ::", matches);
+  console.timeEnd("part 1");
+})();
+
+// Part 2
+(() => {
+  console.time("part 2");
+  let matches = 0;
+  const centerPoints: Coordinate[] = [];
+
+  for (let y = 0; y < HEIGHT; y++) {
+    for (let x = 0; x < WIDTH; x++) {
+      const char = wordsearch[y][x];
+
+      if (char === "A") {
+        centerPoints.push({ x, y });
+      }
+    }
+  }
+
+  for (let i = 0; i < centerPoints.length; i++) {
+    const point = centerPoints[i];
+
+    const topRightCoord = {
+      x: point.x + DIRECTION_MAP.NE.x,
+      y: point.y + DIRECTION_MAP.NE.y,
+    };
+
+    const bottomRightCoord = {
+      x: point.x + DIRECTION_MAP.SE.x,
+      y: point.y + DIRECTION_MAP.SE.y,
+    };
+
+    const bottomLeftCoord = {
+      x: point.x + DIRECTION_MAP.SW.x,
+      y: point.y + DIRECTION_MAP.SW.y,
+    };
+
+    const topLeftCoord = {
+      x: point.x + DIRECTION_MAP.NW.x,
+      y: point.y + DIRECTION_MAP.NW.y,
+    };
+
+    if (
+      isOutOfBounds(topRightCoord) ||
+      isOutOfBounds(bottomRightCoord) ||
+      isOutOfBounds(bottomLeftCoord) ||
+      isOutOfBounds(topLeftCoord)
+    ) {
+      continue;
+    }
+
+    const topLeftChar = wordsearch[topLeftCoord.y][topLeftCoord.x];
+    const bottomLeftChar = wordsearch[bottomLeftCoord.y][bottomLeftCoord.x];
+    const bottomRightChar = wordsearch[bottomRightCoord.y][bottomRightCoord.x];
+    const topRightChar = wordsearch[topRightCoord.y][topRightCoord.x];
+
+    if (
+      ((topLeftChar === "M" && bottomRightChar === "S") ||
+        (topLeftChar === "S" && bottomRightChar === "M")) &&
+      ((bottomLeftChar === "M" && topRightChar === "S") ||
+        (bottomLeftChar === "S" && topRightChar === "M"))
+    ) {
+      matches += 1;
+    }
+  }
+
+  console.log("part 2 matches ::", matches);
+  console.timeEnd("part 2");
+})();

README.md

@@ -6,6 +6,7 @@
 
 |                    Day                    | Part 1 | Part 2 |
 | :---------------------------------------: | :----: | :----: |
+| [04](https://adventofcode.com/2024/day/4) |   ✅   |   ✅   |
 | [03](https://adventofcode.com/2024/day/3) |   ✅   |   ✅   |
 | [02](https://adventofcode.com/2024/day/2) |   ✅   |   ✅   |
 | [01](https://adventofcode.com/2024/day/1) |   ✅   |   ✅   |