【leetcode】Clone Graph

Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors.

OJ‘s undirected graph serialization:

Nodes are labeled uniquely.

We use # as a separator for each node, and , as a separator for node label and each neighbor of the node.

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
         /          \_/

实现一个克隆节点的方法，在这个方法中：

1. 判断这个节点是否被clone过了，如果是，返回它对应的clone节点；
2. 如果没有被clone过，那么新建节点为该节点的clone节点，并且递归的clone它的邻居节点，放入该节点的neighbors列表里面；

代码如下：

 1 /**
 2  * Definition for undirected graph.
 3  * class UndirectedGraphNode {
 4  *     int label;
 5  *     List<UndirectedGraphNode> neighbors;
 6  *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 7  * };
 8  */
 9 public class Solution {
10     private HashMap<UndirectedGraphNode,UndirectedGraphNode> mapClone = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();
11
12     private UndirectedGraphNode cloneNode(UndirectedGraphNode node){
13         if(node == null)
14             return null;
15         //if this node already has a clone
16         if(mapClone.containsKey(node))
17             return mapClone.get(node);
18
19         //if this node hasn‘t been cloned, we construct a new node copy
20         UndirectedGraphNode copy = new UndirectedGraphNode(node.label);
21         mapClone.put(node, copy);
22
23         //clone all the neighbers of node
24         for(UndirectedGraphNode n:node.neighbors){
25             copy.neighbors.add(cloneNode(n));
26         }
27         return copy;
28     }
29     public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
30         return cloneNode(node);
31     }
32 }

【leetcode】Clone Graph