function node (coords) {
    this.x = coords.x;
    this.y = coords.y;
    this.red = 0;
    this.blue = 0;
    this.visit = (color, distance) => {
        this[color] = distance;
    };
    return this;
}

const MOVE = {
    R: (coords) => {return {x: coords.x+1, y: coords.y+0} },
    L: (coords) => {return {x: coords.x-1, y: coords.y+0} },
    U: (coords) => {return {x: coords.x+0, y: coords.y+1} },
    D: (coords) => {return {x: coords.x+0, y: coords.y-1} },
}

const on = (a, b) => a.x === b.x && a.y === b.y

const getClosest = (board) => board.filter((node) => node.red && node.blue)
                                   .map(node => Math.abs(node.x) + Math.abs(node.y))
                                   .sort((a, b) => a.distance-b.distance)[0];

const getClosestBySignal = (board) => board.filter((node) => node.red && node.blue)
                                           .map(node => node.red+node.blue)
                                           .sort((a, b) => a-b)[0];

let board = [];

const traverse = (path, color) => {
    path = path.map(move => { return { direction: move.slice(0, 1),
                                       length: move.slice(1) }});
    let coords = {x: 0, y: 0};
    let index = 0;
    let moves = 0;
    path.forEach(move => {
        for(let i = move.length; i > 0; --i) {
            coords = MOVE[move.direction](coords);
            ++moves;
            let currentNode = board.find(node => on(coords, node));
            if(!currentNode) {
                currentNode = new node(coords);
                board.push(currentNode);
            }
            currentNode.visit(color, moves);
        }
        console.log(`Move ${++index} of ${path.length} completed for ${color}`);
    });
}

traverse(red, "red");
traverse(blue, "blue");
console.log(getClosestBySignal(board));