Reorder Routes to Make All Paths Lead to the City Zero.js

// Runtime: 267 ms (Top 86.1%) | Memory: 107.22 MB (Top 89.0%)

var minReorder = function(n, connections) {
    // from: (<from city>, [<to cities>])
    // to: (<to city>, [<from cities>])
    const from = new Map(), to = new Map();

    // Function to insert in values in map
    const insert = (map, key, value) => {
        if(map.has(key)){
            const arr = map.get(key);
            arr.push(value);
            map.set(key, arr);
        } else {
            map.set(key, [value]);
        }
    }

    // Set all values in both maps
    for(const [a,b] of connections){
        insert(from, a, b);
        insert(to, b, a);
    }

    // Queue: cities to visit
    const queue = [0], visited = new Set();
    let count = 0;

    while(queue.length) {
        const cur = queue.shift(); // First element in queue

        // Check values in first map
        if(from.has(cur)){
            for(const x of from.get(cur)){
                // If visited, do nothing else add to queue
                if(visited.has(x)) continue;
                queue.push(x);
                count++; // Change direction of this path
            }
        }

        if(to.has(cur)){
            // If visited, do nothing else add to queue
            for(const x of to.get(cur)){
                if(visited.has(x)) continue;
                queue.push(x);
            }
        }

        visited.add(cur); // Mark city as visited
    }

    return count
};