naive solution

src/2024/day11.js

@@ -0,0 +1,58 @@
+function next(stone) {
+  if (stone === 0) {
+    return [1];
+  }
+  if (`${stone}`.length % 2 === 0) {
+    const s = `${stone}`;
+    return [
+      parseInt(s.slice(0, s.length / 2)),
+      parseInt(s.slice(s.length / 2)),
+    ];
+  }
+  return [stone * 2024];
+}
+
+const memory = new Map();
+function do25(stone) {
+  if (memory.has(stone)) return memory.get(stone);
+  let stones = [stone];
+  for (let j = 0; j < 25; j++) stones = stones.flatMap(next);
+  memory.set(stone, stones);
+  return stones;
+}
+
+// function doit(stone, times = 25) {
+//   if (times === 0) return 1;
+
+//   const key = `${stone},${times}`;
+//   if (memory.has(key)) return memory.get(key);
+//   let sum = 0;
+//   let stones = next(stone);
+//   stones.forEach(stone => {
+//     sum += doit(stone, times - 1);
+//   });
+//   memory.set(key, sum);
+//   return sum;
+// }
+
+export function part1(input) {
+  let stones = input.split(" ").map(Number);
+  let sum = 0;
+  stones.forEach(stone => {
+    sum += do25(stone).length;
+  });
+  return sum;
+}
+
+export function part2(input) {
+  let stones = input.split(" ").map(Number);
+  let sum = 0;
+  stones.forEach(stone => {
+    do25(stone).forEach(stone => {
+      do25(stone).forEach(stone => {
+        sum += do25(stone).length;
+      });
+    });
+  });
+  return sum;
+}

src/2024/day11.spec.js

@@ -0,0 +1,26 @@
+import { part1, part2 } from "./day11.js";
+import readInput from "../utils/read-input.js";
+
+const input = readInput(import.meta.url);
+
+describe("day11 2024", () => {
+  describe("part1", () => {
+    test("it should work for part 1 examples", () => {
+      expect(part1(["125 17"].join("\n"))).toEqual(55312);
+    });
+
+    test("it should work for part 1 input", () => {
+      expect(part1(input)).toEqual(197157);
+    });
+  });
+
+  describe("part2", () => {
+    test("it should work for part 2 examples", () => {
+      // expect(part2(paste)).toEqual(paste);
+    });
+
+    test("it should work for part 2 input", () => {
+      expect(part2(input)).toEqual(234430066982597);
+    });
+  });
+});

src/2024/day11.txt

@@ -0,0 +1,2 @@
+0 44 175060 3442 593 54398 9 8101095
+