https://leetcode.com/problems/shortest-path-with-alternating-colors/

shortestPathWithAlternatingColours.js

var shortestAlternatingPaths = function(n, red_edges, blue_edges) {
    
    const reds = {}; const blues= {};
    red_edges.forEach(([from, to]) => {
        reds[from] = reds[from] || new Set();
        reds[from].add(to);
    });
    blue_edges.forEach(([from, to]) => {
        blues[from] = blues[from] || new Set();
        blues[from].add(to);
    });
    
    const result = new Array(n).fill(-1);
    const queue = [{node: 0, red: true, dist: 0}, {node: 0, red: false, dist: 0}];
    const visited = new Map(); // `node:fromColour` : dist

    while(queue.length){
        const {node, red, dist} = queue.shift();
        if(result[node] === -1) result[node] = dist;
        if(visited.has(`${node}:${red}`)) continue;
        visited.set(`${node}:${red}`, node);

        const siblings = (red ? blues : reds)[node] || new Set();
        for(let to of siblings){
            if(!visited.has(`${to}:${red ? 0 : 1}`)){
                queue.push({node: to, red: red ? 0 : 1, dist: dist + 1});
            }
        }
    }

    return result;
};