Discussion on: AoC Day 14: Chocolate Charts

[Tiago Romero Garcia]

JavaScript solution

I did Part 1 using arrays and I attempted Part 2 using indexOf to locate the input inside the array.

I was getting memory errors, so I wrote an algorithm that would always attempt to find the input as the last N elements of the scorecard, backwards. With a few optimizations, it runs in 5 seconds!

14a.js

const getScoreBoard = input => {
    const scoreboard = [3, 7];
    let elf1 = 0;
    let elf2 = 1;

    while (scoreboard.length < input + 10) {
        const scoreElf1 = scoreboard[elf1];
        const scoreElf2 = scoreboard[elf2];
        const newRecipes = (scoreElf1 + scoreElf2).toString().split('').map(i => +i);
        scoreboard.push(...newRecipes);

        const { length } = scoreboard;
        elf1 = (elf1 + scoreElf1 + 1) % length;
        elf2 = (elf2 + scoreElf2 + 1) % length;
    }

    return scoreboard;
};

(() => {
    const input = 880751;
    const scoreboard = getScoreBoard(input);
    const scores = scoreboard.slice(input, input + 10).join('');

    console.log(`The scores of the ten recipes immediately after the given number of recipes is ${scores}`);
})();

14b.js

const numberOfRecipes = input => {
    const scoreboard = [3, 7];
    let elf1 = 0;
    let elf2 = 1;

    input = input.split('').map(i => +i);
    const n = input.length;
    let m = scoreboard.length;

    let number;
    while (!number) {
        const scoreElf1 = scoreboard[elf1];
        const scoreElf2 = scoreboard[elf2];

        const newRecipes = (scoreElf1 + scoreElf2).toString().split('').map(i => +i);
        scoreboard.push(...newRecipes);
        m += newRecipes.length;

        const { length } = scoreboard;
        elf1 = (elf1 + scoreElf1 + 1) % length;
        elf2 = (elf2 + scoreElf2 + 1) % length;

        let foundInput = false;
        for (let tries = 0; !foundInput && tries < newRecipes.length; tries++) {
            let hasNotFoundInputYet = false;
            for (let i = 1; !hasNotFoundInputYet && i <= n; i++) {
                if (scoreboard[m-i-tries] !== input[n-i]) {
                    hasNotFoundInputYet = true;
                }
            }
            foundInput = !hasNotFoundInputYet;
        }

        if (foundInput) {
            number = m - n;
        } 
    }

    return number;
};

(() => {
    const input = '880751';
    const number = numberOfRecipes(input);

    console.log(`The number of recipes which appear on the scoreboard to the left of input is ${number}`);
})();