feat: 2024 Day 18

Author: mfulton26

2024/day/18/part/1/solve.test.ts

@@ -0,0 +1,34 @@
+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0`;
+
+  assertEquals(solve(input, { size: 7, bytes: 12 }), 22);
+});

2024/day/18/part/1/solve.ts

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+const directions = [[0, -1], [0, 1], [-1, 0], [1, 0]];
+
+function findLeastTimeToExit(
+  locations: readonly number[][],
+  size: number,
+  bytes: number,
+) {
+  const grid = Array.from(
+    { length: size },
+    () => Array.from({ length: size }),
+  );
+  for (let byte = 0; byte < bytes; byte++) {
+    const [x, y] = locations[byte];
+    grid[y][x] = "#";
+  }
+  const xf = size - 1, yf = xf;
+  const queue = [[0, 0, 0]];
+  const seen = new Set<`${number},${number}`>();
+  while (queue.length) {
+    const [x, y, t] = queue.shift()!;
+    if (!(y in grid) || !(x in grid[y]) || grid[y][x] === "#") continue;
+    if (x === xf && y === yf) return t;
+    const hash = `${x},${y}` as const;
+    if (seen.has(hash)) continue;
+    seen.add(hash);
+    for (const [dx, dy] of directions) queue.push([x + dx, y + dy, t + 1]);
+  }
+}
+
+export default function solve(input: string, { size = 71, bytes = 1024 } = {}) {
+  const locations = input.split("\n")
+    .map((line) => line.split(",").map(Number));
+  return findLeastTimeToExit(locations, size, bytes);
+}

2024/day/18/part/2/solve.test.ts

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+import solve from "./solve.ts";
+
+import { assertEquals } from "@std/assert";
+
+Deno.test("example", () => {
+  const input = `\
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0`;
+
+  assertEquals(solve(input, { size: 7 }), "6,1");
+});

2024/day/18/part/2/solve.ts

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+const directions = [[0, -1], [0, 1], [-1, 0], [1, 0]];
+
+function findLeastTimeToExit(
+  locations: readonly number[][],
+  size: number,
+  bytes: number,
+) {
+  const grid = Array.from(
+    { length: size },
+    () => Array.from({ length: size }),
+  );
+  for (let byte = 0; byte < bytes; byte++) {
+    const [x, y] = locations[byte];
+    grid[y][x] = "#";
+  }
+  const xf = size - 1, yf = xf;
+  const queue = [[0, 0, 0]];
+  const seen = new Set<`${number},${number}`>();
+  while (queue.length) {
+    const [x, y, t] = queue.shift()!;
+    if (!(y in grid) || !(x in grid[y]) || grid[y][x] === "#") continue;
+    if (x === xf && y === yf) return t;
+    const hash = `${x},${y}` as const;
+    if (seen.has(hash)) continue;
+    seen.add(hash);
+    for (const [dx, dy] of directions) queue.push([x + dx, y + dy, t + 1]);
+  }
+}
+
+export default function solve(input: string, { size = 71 } = {}) {
+  const locations = input.split("\n")
+    .map((line) => line.split(",").map(Number));
+  let low = 0, high = locations.length - 1;
+  while (low <= high) {
+    const mid = Math.floor((low + high) / 2);
+    const t = findLeastTimeToExit(locations, size, mid);
+    if (t === undefined) {
+      high = mid - 1;
+    } else {
+      low = mid + 1;
+    }
+  }
+  return locations[high].join(",");
+}