Clone Graph

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        Queue<UndirectedGraphNode> queue = new LinkedList<>();
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<>();
        UndirectedGraphNode cloneNode = new UndirectedGraphNode(node.label);
        map.put(node, cloneNode);
        queue.offer(node);
        while (!queue.isEmpty()) {
            UndirectedGraphNode n = queue.poll();
            UndirectedGraphNode nCopy = map.get(n);
            List<UndirectedGraphNode> neighbors = n.neighbors;
            for (UndirectedGraphNode neighbor: neighbors) {
                if (!map.containsKey(neighbor)) {
                    UndirectedGraphNode copyNeighbor = new UndirectedGraphNode(neighbor.label);
                    nCopy.neighbors.add(copyNeighbor);
                    queue.offer(neighbor);
                    map.put(neighbor, copyNeighbor);
                } else {
                    UndirectedGraphNode copyNeighbor = map.get(neighbor);
                    nCopy.neighbors.add(copyNeighbor);
                }
            }
        }
        return cloneNode;
    }
}