day 11 (#24)

days/11/main.ts

@@ -0,0 +1,58 @@
+import { loadInput } from "utils";
+
+export function part1(input: Array<string>) {
+  const stones = parseInput(input);
+  const blink25 = blink(25);
+  return stones.map(blink25).reduce((a, b) => a + b);
+}
+
+export function part2(input: Array<string>) {
+  const stones = parseInput(input);
+  const blink75 = blink(75);
+  return stones.map(blink75).reduce((a, b) => a + b);
+}
+
+function blink(times: number) {
+  const cache = new Map<string, number>();
+  return (stone: number) => blinkRec(stone, times, cache);
+}
+
+function blinkRec(
+  stone: number,
+  times: number,
+  cache: Map<string, number>,
+): number {
+  if (times === 0) {
+    return 1;
+  }
+  const cacheHit = cache.get(`${stone}-${times}`);
+  if (cacheHit != null) {
+    return cacheHit;
+  }
+  if (stone === 0) {
+    const result = blinkRec(1, times - 1, cache);
+    cache.set(`${stone}-${times}`, result);
+    return result;
+  }
+  const str = stone.toString();
+  if (str.length % 2 === 0) {
+    const half = str.length / 2;
+    const left = blinkRec(parseInt(str.slice(0, half), 10), times - 1, cache);
+    const right = blinkRec(parseInt(str.slice(half), 10), times - 1, cache);
+    const result = left + right;
+    cache.set(`${stone}-${times}`, result);
+    return result;
+  }
+  const result = blinkRec(stone * 2024, times - 1, cache);
+  cache.set(`${stone}-${times}`, result);
+  return result;
+}
+
+function parseInput(input: Array<string>): Array<number> {
+  return input[0].split(" ").map(Number);
+}
+
+if (import.meta.main) {
+  console.log(part1(await loadInput(11)));
+  console.log(part2(await loadInput(11)));
+}

days/11/main_test.ts

@@ -0,0 +1,26 @@
+import { expect } from "@std/expect";
+import { describe, it } from "@std/testing/bdd";
+import { part1, part2 } from "./main.ts";
+import { loadInput } from "utils";
+
+describe("day 11 example", () => {
+  const input = ["125 17"];
+
+  it("part 1", () => {
+    expect(part1(input)).toBe(55312);
+  });
+
+  it("part 2", () => {
+    expect(part2(input)).toBe(65601038650482);
+  });
+});
+
+describe("day 11 solution", () => {
+  it("part 1", async () => {
+    expect(part1(await loadInput(11))).toBe(239714);
+  });
+
+  it("part 2", async () => {
+    expect(part2(await loadInput(11))).toBe(284973560658514);
+  });
+});

days/mod.ts

@@ -3,7 +3,7 @@ type Solution = { part1: PartFunction; part2: PartFunction };
 
 const days = new Map<number, Solution>();
 
-for (const day of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) {
+for (const day of [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]) {
   days.set(day, await import(`./${day}/main.ts`));
 }