1 /**
 2  * Definition for undirected graph.
 3  * class UndirectedGraphNode {
 4  *     int label;
 5  *     ArrayList<UndirectedGraphNode> neighbors;
 6  *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 7  * };
 8  */
 9 public class Solution {
10     public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
11         // Note: The Solution object is instantiated only once and is reused by each test case.
12         if(node == null){
13             return node;
14         }
15         UndirectedGraphNode result = new UndirectedGraphNode(node.label);
16         LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
17         queue.add(node);
18         Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
19         map.put(node, result);
20
21         while(!queue.isEmpty()){
22             UndirectedGraphNode nodeInQueue = queue.poll();
23             ArrayList<UndirectedGraphNode> neighbors = nodeInQueue.neighbors;
24             for(int i = 0; i < neighbors.size(); i++){
25                 UndirectedGraphNode n1 = neighbors.get(i);
26                 if(map.containsKey(n1)){
27                     map.get(nodeInQueue).neighbors.add(map.get(n1));
28                 } else {
29                     UndirectedGraphNode n1clone = new UndirectedGraphNode(n1.label);
30                     map.get(nodeInQueue).neighbors.add(n1clone);
31                     map.put(n1, n1clone);
32                     queue.add(n1);
33                 }
34             }
35
36         }
37         return result;
38     }
39 }