Day 11 Part 2

2024/11/index.ts

@@ -8,32 +8,43 @@ const countMap: { [key: string]: Array<number> } = {};
 
 let sum = 0;
 
-function getCountAfter(stone: string, blink: number) {
-    const newStones: Array<string> = [];
-    stones.forEach((stone) => {
-        if (stone === '0') {
-            newStones.push('1');
-            return;
+function getCountAfter(stone: string, blink: number, prev: Array<string> = []): number {
+    const nextStep = blink - 1;
+    if (countMap[stone]) {
+        if (countMap[stone][nextStep]) {
+            return countMap[stone][nextStep];
         }
+    } else {
+        countMap[stone] = [];
+    }
+    let newStones: Array<string>;
+    if (stone === '0') {
+        newStones = ['1'];
+    } else {
         const len = stone.length;
         if (len % 2 === 0) {
-            newStones.push(stone.slice(0, len / 2));
             let last = stone.slice(len / 2);
-            newStones.push(''+(parseInt(last)));
-            return;
+            newStones = [stone.slice(0, len / 2), ''+parseInt(last)];
+        } else {
+            newStones = [''+(parseInt(stone) * 2024)];
         }
-        newStones.push(''+(parseInt(stone) * 2024));
-    });
-    if (blink === 1) {
-        return newStones;
     }
-    return newStones.sum((newStone) => getCountAfter(newStone, blink - 1));
+    const len = newStones.length;
+    countMap[stone][0] = len;
+    if (blink === 1) {
+        return len;
+    } else {
+        const newPrev = [...prev, stone];
+        const len = newStones.reduce((carry, newStone) => carry + getCountAfter(newStone, nextStep, newPrev), 0);
+        countMap[stone][nextStep] = len;
+        return len;
+    }
 }
 
-const blinks = 25;
+const blinks = 75;
 
 stones.forEach((stone) => {
-    sum += getCountAfter(stone, 25);
+    sum += getCountAfter(stone, blinks);
 });
 
 console.log(sum);