Clone Graph - Rainee

/**
 * 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<UndirectedGraphNode>();
        Map<UndirectedGraphNode,UndirectedGraphNode> hash = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
        
        queue.add(node);
        UndirectedGraphNode cloneNode = new UndirectedGraphNode(node.label);
        hash.put(node,cloneNode);
        
        while(!queue.isEmpty()) {
            UndirectedGraphNode oldNode = queue.remove();
            UndirectedGraphNode newNode = hash.get(oldNode);
            
            for(int i = 0; i < oldNode.neighbors.size(); i++) {
                UndirectedGraphNode temp = oldNode.neighbors.get(i);
                if(hash.containsKey(temp)) {
                    newNode.neighbors.add(hash.get(temp));
                }else {
                    UndirectedGraphNode newcloneNode = new UndirectedGraphNode(temp.label);
                    queue.add(temp);
                    hash.put(temp,newcloneNode);
                    newNode.neighbors.add(newcloneNode);
                }
            }
        }
        return cloneNode;
    }
}