adventofcode_day7.js

// reduce function returning all directories bigger than 100K
const reduceToBiggerThan = (list, directory) => {
    if (directory.size <= 100 * 1000) {
        list.push(directory);
    }
    directory.children.reduce(reduceToBiggerThan, list);
    return list;
}

// reduce to the smallest directory that is bigger than the neededSpace
const reduceToSmallestDelete =  (neededSpace) => {
    return function reduceToSmallest(topCandidate, directory) {
        // too small, don't bother with children
        if (directory.size < neededSpace) {
            return topCandidate;
        }
        // go depth first
        topCandidate = directory.children.reduce(reduceToSmallest, topCandidate);
        if (!topCandidate || directory.size < topCandidate.size) {
            return directory
        }
        return topCandidate;
    }
};

function Directory(parent) {;
    this.parent = parent;
    this.children = [];
    this.size = 0;
    this.addFile = (size) => {
        this.size += size;
        this.parent && this.parent.addFile(size);
    }
    return this;
}

const main = (inputString) => {
    const topDirectory = new Directory();
    let currentDirectory = topDirectory;
    inputString.split('\n').forEach(line => {
        const parts = line.split(' ');
        const firstWord = parts[0];
        const directoryName = parts[2];
        switch (firstWord) {
            case '$':
                // if directoryName is not set, it's a `ls` cmd which
                // we ignore. we also ignore `cd /`, it happens only once at start
                if (directoryName == '..') {
                    currentDirectory = currentDirectory.parent;
                } else if (directoryName) {
                    // a directory is never entered twice, so we can simply create
                    // when entered
                    const newDirectory = new Directory(currentDirectory);
                    currentDirectory.children.push(newDirectory)
                    currentDirectory = newDirectory;
                }
                break;
            case 'dir':
                // dont care but don't fall into default
                break;
            default:
                // must be file at at this point
                const fileSize = parseInt(firstWord);
                currentDirectory.addFile(fileSize);
        }
    });
   


    const directoriesBiggerThan = topDirectory.children.reduce(reduceToBiggerThan, []);
    const sum = directoriesBiggerThan.reduce((prev, current) => {
        return prev + current.size;
    }, 0);
    console.log('part 1', sum);

    const usedSpace = topDirectory.size;
    const freeSpace = 70000000 - usedSpace;
    const neededSpace = 30000000 - freeSpace;
    
    const bestDirectory = topDirectory.children.reduce(reduceToSmallestDelete(neededSpace), null);
    console.log('part 2', bestDirectory.size)
}