2024D11: Part 2

2024/src/2024/day11/day11.test.ts

@@ -1,4 +1,4 @@
-import {blink, part1, part2} from "./day11";
+import {blinkV1, part1, part2} from "./day11";
 
 const input = "41078 18 7 0 4785508 535256 8154 447";
 const testInput1 = "0 1 10 99 999";
@@ -11,13 +11,13 @@ describe('2024 Day 11', () => {
     });
 
     test('Part 2', async () => {
-        expect(await part2(input)).toEqual(217443);
+        expect(await part2(input)).toEqual(257246536026785);
     });
 });
 
 test('blink', () => {
-    expect(blink(testInput1).join(" ")).toEqual("1 2024 1 0 9 9 2021976")
-    expect(blink(testInput2).join(" ")).toEqual("253000 1 7")
-    expect(blink(blink(testInput2)).join(" ")).toEqual("253 0 2024 14168")
-    expect(blink(blink(blink(testInput2))).join(" ")).toEqual("512072 1 20 24 28676032")
+    expect(blinkV1(testInput1).join(" ")).toEqual("1 2024 1 0 9 9 2021976")
+    expect(blinkV1(testInput2).join(" ")).toEqual("253000 1 7")
+    expect(blinkV1(blinkV1(testInput2)).join(" ")).toEqual("253 0 2024 14168")
+    expect(blinkV1(blinkV1(blinkV1(testInput2))).join(" ")).toEqual("512072 1 20 24 28676032")
 });

2024/src/2024/day11/day11.ts

@@ -1,32 +1,49 @@
-
 export async function part1(inputString: string) {
-    return await day11(inputString, 25);
+    return day11(inputString, 25);
 }
 
 export async function part2(inputString: string) {
-    return await day11(inputString, 75);
+    return day11(inputString, 75);
 }
 
 async function day11(inputString: string, times: number) {
     return calcBlinkOutput(inputString.split(" "), times);
 }
 
 function calcBlinkOutput(stones: string[], times: number) {
-    let expandedStonesCount= 0;
+    let stoneCounts: Map<string, number> = new Map();
 
     stones.forEach(stone => {
-        expandedStonesCount += blinkNtimes([stone], times);
-    })
-
-    return expandedStonesCount;
-}
+        stoneCounts.set(stone, (stoneCounts.get(stone) || 0) + 1);
+    });
 
-function blinkNtimes(stones: string[], times: number) {
-    let expandedStones = [...stones];
     for (let i = 0; i < times; i++) {
-        expandedStones = blink(expandedStones);
+        stoneCounts = blink(stoneCounts);
     }
-    return expandedStones.length;
+
+    return Array.from(stoneCounts.values())
+        .reduce((sum, count) => sum + count, 0);
+}
+
+function blink(stoneCounts: Map<string, number>): Map<string, number> {
+    const newStoneCounts: Map<string, number> = new Map();
+
+    stoneCounts.forEach((count, stone) => {
+        if (stone === '0') {
+            newStoneCounts.set('1', (newStoneCounts.get('1') || 0) + count);
+        } else if (stone.length % 2 === 0) {
+            const half = stone.length / 2;
+            const first = Number.parseInt(stone.slice(0, half)) + '';
+            const second = Number.parseInt(stone.slice(half)) + '';
+            newStoneCounts.set(first, (newStoneCounts.get(first) || 0) + count);
+            newStoneCounts.set(second, (newStoneCounts.get(second) || 0) + count);
+        } else {
+            const multiplied = (Number.parseInt(stone) * 2024) + '';
+            newStoneCounts.set(multiplied, (newStoneCounts.get(multiplied) || 0) + count);
+        }
+    });
+
+    return newStoneCounts;
 }
 
 // Every time you blink, the stones each simultaneously change according to the _first applicable_ rule in this list:
@@ -36,7 +53,7 @@ function blinkNtimes(stones: string[], times: number) {
 //    The left half of the digits are engraved on the new left stone, and the right half of the digits are engraved on the new right stone.
 // 3. If none of the other rules apply, the stone is replaced by a new stone;
 //    the old stone's number multiplied by 2024 is engraved on the new stone.
-export function blink(stones: string[] | string): string[] {
+export function blinkV1(stones: string[] | string): string[] {
     const inputStones = typeof stones === 'string' ? stones.split(" ") : stones;
     const updatedStones: string[] = [];