Javascript

Spent 10 minutes debugging my solution until I reread and found out they wanted the number of keys that fit, not the ones that overlapped. Reading comprehension is not it tonight.

const [locks, keys] = require('fs').readFileSync(0, 'utf-8').split(/\r?\n\r?\n/g).filter(v => v.length > 0).map(s => s.split(/\r?\n/g).filter(v => v.length > 0)).reduce((acc, s) => {
    const lock = s[0].split('').every(v => v === '#');
    const schema = s.slice(1, -1);
    let rotated = [];
    for (let i = 0; i < schema[0].length; i += 1) {
        for (let j = 0; j < schema.length; j += 1) {
            if (!rotated[i]) rotated[i] = [];
            rotated[i].push(schema[j][i]);
        }
    }
    if (!lock) {
        rotated = rotated.map(v => v.reverse());
    }
    const pinHeights = [];
    for (const row of rotated) {
        const height = row.indexOf('.');
        pinHeights.push(height !== -1 ? height : 5);
    }
    if (lock) {
        acc[0].push(pinHeights);
    } else {
        acc[1].push(pinHeights);
    }
    return acc;
}, [[],[]]);

let fits = 0;
for (const lock of locks) {
    for (const key of keys) {
        let overlapped = false;
        for (let i = 0; i < lock.length; i += 1) {
            if ((lock[i] + key[i]) > 5) {
                overlapped = true;
            }
        }
        if (!overlapped) {
            fits += 1;
        }
    }
}

console.log('Part One', fits);