adventofcode_day5.js

const parse = (inputString) => {
    const lines = inputString.split('\n');
    const crateLines = lines.slice(0,8);
    const moveLines = lines.slice(10);
    const crates = [];
    crateLines.forEach(crateLine => {
        let columnIdx = 0;
        for (let i=1;i<crateLine.length-1;i+=4) {
            let crateChar = crateLine.slice(i, i+1);
            crates[columnIdx] = crates[columnIdx] || [];
            if (crateChar != ' ') {
                crates[columnIdx].push(crateChar);
            }            
            columnIdx++;
        }
    });
    const moves = [];
    moveLines.forEach(move => {
        let parts = move.split(' ');
        moves.push({
            count: parseInt(parts[1]),
            from: parseInt(parts[3]) - 1,
            to: parseInt(parts[5]) - 1
        })
    })
    return {crates, moves};
}

const moveCrates = ({crates, moves, sameOrder}) => {
    moves.forEach(move => {
        const cratesToMove = crates[move.from].splice(0, move.count);
        if (!sameOrder) {
            cratesToMove.reverse();
        }
        Array.prototype.unshift.apply(crates[move.to], cratesToMove);
    });
    return crates;
}

const mainDayFiveA = (inputString) => {
    const {crates, moves} = parse(inputString);
    const movedCrates = moveCrates({crates, moves, sameOrder: false});
    return movedCrates.map(column => {
        return column[0]
    }).join('')
}

const mainDayFiveB = (inputString) => {
    const {crates, moves} = parse(inputString);
    const movedCrates = moveCrates({crates, moves, sameOrder: true});
    return movedCrates.map(column => {
        return column[0]
    }).join('')
}