Problem Clone Graph

Problem Description:

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

Solution:

    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if (node == null) {
            return null;
        }
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        queue.add(node);
        while (!queue.isEmpty()) {
            UndirectedGraphNode q = queue.poll();
            UndirectedGraphNode newNode = new UndirectedGraphNode(q.label);
            map.put(q, newNode);
            for (UndirectedGraphNode neighbor : q.neighbors) {
                if (!map.containsKey(neighbor)) {
                    queue.add(neighbor);
                }
            }
        }
        Set<UndirectedGraphNode> keySet = map.keySet();
        for (UndirectedGraphNode p : keySet) {
            UndirectedGraphNode n  = map.get(p);
            for (UndirectedGraphNode q : p.neighbors) {
                n.neighbors.add(map.get(q));
            }
        }

        return map.get(node);
    }