AoC/2024/11/index.ts

const fs = require('fs');

const input = fs.readFileSync(__dirname + '/input.txt', 'utf8');

let stones: Array<string> = input.slice(0, -1).split(' ');

const countMap: { [key: string]: Array<number> } = {};

let sum = 0;

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) {
            let last = stone.slice(len / 2);
            newStones = [stone.slice(0, len / 2), ''+parseInt(last)];
        } else {
            newStones = [''+(parseInt(stone) * 2024)];
        }
    }
    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 = 75;

stones.forEach((stone) => {
    sum += getCountAfter(stone, blinks);
});

console.log(sum);