Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors. OJ's un

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     ArrayList<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */
import java.util.*;
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node == null ){
            return null;
        }
        Map<UndirectedGraphNode,UndirectedGraphNode> map = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
        return clone(node,map);
    }
    public UndirectedGraphNode clone(UndirectedGraphNode node, Map<UndirectedGraphNode,UndirectedGraphNode> map){
        if(node == null){
            return null;
        }
        if(map.containsKey(node)){
            return map.get(node);
        }
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        map.put(node,newNode);
        for(UndirectedGraphNode n : node.neighbors){
            newNode.neighbors.add(clone(n,map));
        }
        return newNode;
    }
}