memoized solution

src/2024/day11.js

@@ -13,46 +13,26 @@ function next(stone) {
 }
 
 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;
+function doit(stone, times) {
+  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);
+  const key = `${stone},${times}`;
+  if (memory.has(key)) return memory.get(key);
   let sum = 0;
+  let stones = next(stone);
   stones.forEach(stone => {
-    sum += do25(stone).length;
+    sum += doit(stone, times - 1);
   });
+  memory.set(key, sum);
   return sum;
 }
 
+export function part1(input) {
+  let stones = input.split(" ").map(Number);
+  return stones.reduce((sum, stone) => sum + doit(stone, 25), 0);
+}
+
 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;
+  return stones.reduce((sum, stone) => sum + doit(stone, 75), 0);
 }