cloneGraph.js

/*
https://leetcode.com/problems/clone-graph/

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.

class Node {
    public int val;
    public List<Node> neighbors;
}

Test case format:

For simplicity, each node's value is the same as the node's index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

Example 1:
Input: adjList = [[2,4],[1,3],[2,4],[1,3]]
Output: [[2,4],[1,3],[2,4],[1,3]]
Explanation: There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).

Example 2:
Input: adjList = [[]]
Output: [[]]
Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

Example 3:
Input: adjList = []
Output: []
Explanation: This an empty graph, it does not have any nodes.

Constraints:
The number of nodes in the graph is in the range [0, 100].
1 <= Node.val <= 100
Node.val is unique for each node.
There are no repeated edges and no self-loops in the graph.
The Graph is connected and all nodes can be visited starting from the given node.
*/

class Node {
    constructor(val, neighbors) {
        this.val = val === undefined ? 0 : val;
        this.neighbors = neighbors === undefined ? [] : neighbors;
    }
}

const cloneGraph = (node) => {
    if (!node) {
        return node
    }

    const root = new Node(node.val);
    const cache = { [node.val]: root };
    const tracker = [[node.val, node.neighbors]];

    while (tracker.length > 0) {
        const [val, neighbors] = tracker.pop();
        const newNode = cache[val] ?? new Node(val);
        cache[val] = newNode;

        neighbors.forEach(neighbor => {
            const newNeighbor = cache[neighbor.val] ?? new Node(neighbor.val);
    
            if (!cache[neighbor.val]) {
                tracker.push([neighbor.val, neighbor.neighbors]);
            }
    
            newNode.neighbors.push(newNeighbor);
            cache[newNeighbor.val] = newNeighbor;
        });
    }

    return root;
}

module.exports = { cloneGraph, Node };