AoC day 24

d24.js

let dir = {
    'ne': [  1,  1 ],
    'nw': [  -1, 1 ],
    'se': [  1, -1 ],
    'sw': [ -1, -1 ],
    'e':  [  2,  0 ],
    'w':  [ -2,  0 ],
    ' ':  [  0,  0 ]
};

function coords(t) {
    let steps = t.matches(/ne|nw|se|sw|e|w/);
    return [dir[s] for s in steps].fold((a, b) -> a.zip(b, < + >));
}

function nbh(t) {
    return { t.zip(d, < + >) for _, d in dir };
}

let black = { g[0] for g in slurp().lines().map(coords).sort().group() | g.len() % 2 };

/* part 1 */
print(black.len());

for _ in ..100 {
    let check, new = {}, {};
    for t in black { check += nbh(t); }
    for t in check {
        let nc = nbh(t).keys().countBy(|black ? #|);
        if (nc == 2 || ((black ? t) && nc == 3))
            new << t;
    }
    black = new;
}

/* part 2 */
print(black.len());