Nodes are labeled uniquely.

As an example, consider the serialized graph {0,1,2#1,2#2,2}.

The graph has a total of three nodes, and therefore contains three parts as separated by #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. Third node is labeled as 2. Connect node 2 to node 2 (itself), thus forming a self-cycle.

Visually, the graph looks like the following:

       1
      /      /       0 --- 2
         /          \_/

/**
 * 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 node;
        }
        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        Map<Integer, UndirectedGraphNode> map = new HashMap<Integer, UndirectedGraphNode>();
        Set<Integer> deal = new HashSet<Integer>();
        queue.add(node);
        while (queue.size() > 0)
        {
            UndirectedGraphNode p = queue.poll();
            for (UndirectedGraphNode neighbor : p.neighbors)
            {
                if (!map.containsKey(neighbor.label))
                {
                    queue.add(neighbor);
                }
            }
            map.put(p.label, new UndirectedGraphNode(p.label));
        }
        queue.add(node);
        while (queue.size() > 0)
        {
            UndirectedGraphNode p = queue.poll();
            if(deal.contains(p.label))
            {
                continue;
            }
            for (UndirectedGraphNode neighbor : p.neighbors)
            {
                map.get(p.label).neighbors.add(map.get(neighbor.label));
                if (!deal.contains(neighbor.label))
                {
                    queue.add(neighbor);
                }
            }
            deal.add(p.label);
        }
        return map.get(node.label);
    }
}