clone graph

public UndirectedGraphNode (UndirectedGraphNode node) {
    if (node == null)
        return node;
    HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new  HashMap<>();
    Queue<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();
    map.put(node, new UndirectedGraphNode(node.label));
    q.offer(node);
    while (!q.isEmpty()) {
        UndirectedGraphNode cur = q.poll();
        for (UndirectedGraphNode n : cur.neighbors) {
            if (map.containsKey(n))
                continue;
            map.put(n, new UndirectedGraphNode(n.label));
            q.offer(n);
        }
    }
    q.offer(node);
    HashSet<UndirectedGraphNode> set = new HashSet<>();
    set.add(node);
    while (!q.isEmpty()) {
        UndirectedGraphNode cur = q.poll();
        UndirectedGraphNode newNode = map.get(cur);
        for (UndirectedGraphNode n : cur.neighbors) {
            newNode.neighbors.add(map.get(n));
            if (set.contains(n))
                continue;
            set.add(n);
            q.offer(n);
        }
    }
    return map.get(node);
}

for (Map.Entry<UndirectedGraphNode, UndirectedGraphNode> entry : map.entrySet()) {
    UndirectedGraphNode element = entry.getKey();
    for (UndirectedGraphNode neighbor : element.neighbors) {
        map.get(element).neighbors.add(map.get(neighbor));
    }
}
return map.get(node);