adventofcode_day4.js

const parse = (inputString) => {
    const lines = inputString.split('\n');
    return lines.map(line => {
        const parts = line.split(',');
        const partsA = parts[0].split('-').map(i => parseInt(i));
        const partsB = parts[1].split('-').map(i => parseInt(i));
        return {
            a: {
                from: partsA[0],
                to: partsA[1]
            },
            b: {
                from: partsB[0],
                to: partsB[1]
            }
        }
    });
}

const findTotalOverlaps = (pairs) => {
    return pairs.filter(({a, b}) => {
        return (
            a.from <= b.from && a.to >= b.to
        ) || (
            a.from >= b.from && a.to <= b.to
        )
    })
};

const partialOverlap = (pairs) => {
    return pairs.filter(({a, b}) => {
        return a.from <= b.to && b.from <= a.to 
        
    })
}

const mainDayFourA = (inputString) => {
    const pairs = parse(inputString);
    const totalOverlapPairs = findTotalOverlaps(pairs);
    return totalOverlapPairs.length;
}

const mainDayFourB = (inputString) => {
    const pairs = parse(inputString);
    const partialOverlaps = partialOverlap(pairs);
    return partialOverlaps.length; 
}