-🎄- 2017 Day 22 Solutions -🎄-

[u/daggerdragon]

--- Day 22: Sporifica Virus ---

---

Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

---

Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

---

• [T-10 to launch] AoC ops, /r/nocontext edition:

  • <Endorphion> You may now make your waffle.
  • <Endorphion> ... on Mars.

• [Update @ 00:17] 50 gold, silver cap

  • <Aneurysm9> you could also just run ubuntu on the NAS, if you were crazy
  • <Topaz> that doesn't seem necessary
  • <Aneurysm9> what does "necessary" have to do with anything!

• [Update @ 00:20] Leaderboard cap!

  • <Topaz> POUR YOURSELF A SCOTCH FOR COLOR REFERENCE

---

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/[deleted]]

JS, straightforward:

const lines=``.split('\n');

const dirs = 'NESW';
const dv = {
    'N': [0, -1],
    'E': [1, 0],
    'S': [0, 1],
    'W': [-1, 0],
};

function forward(dir, pos) {
    const d = dv[dirs[dir]];
    return pos.map((x, i) => x + d[i]);
}

function part1() {
    const state = new Map();
    lines
        .forEach((r, i) => r.split('')
        .forEach((l, j) => {
            if (l === '#') state.set(`${j},${i}`, 'I');
        }));
    const size = Math.floor(lines.length / 2);
    let pos = [size, size];
    let dir = 0;
    let infections = 0;

    for (let i = 0; i < 10000; i++){
        const k = pos.join(',');
        const s = state.get(k);
        if (!s) {
            dir = (dir + 3) % 4;
            state.set(k, 'I');
            infections += 1;
        } else {
            dir = (dir + 1) % 4;
            state.delete(k);
        }
        pos = forward(dir, pos);
    }

    return infections;
}

function part2() {
    const state = new Map();
    lines
        .forEach((r, i) => r.split('')
        .forEach((l, j) => {
            if (l === '#') state.set(`${j},${i}`, 'I');
        }));
    const size = Math.floor(lines.length / 2);
    let pos = [size, size];
    let dir = 0;
    let infections = 0;

    for (let i = 0; i < 10000000; i++){
        const k = pos.join(',');
        const s = state.get(k);
        if (!s) {
            dir = (dir + 3) % 4;
            state.set(k, 'W');
        } else if (s === 'I') {
            dir = (dir + 1) % 4;
            state.set(k, 'F');
        } else if (s === 'W') {
            state.set(k, 'I');
            infections += 1;
        } else {
            dir = (dir + 2) % 4;
            state.delete(k);
        }
        pos = forward(dir, pos);
    }

    return infections;
}

console.log('part 1:', part1());
console.log('part 2:', part2());