【Leetcode】 Clone Graph

题目链接：https://leetcode.com/problems/clone-graph/

题目：

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
         / \
         \_/

思路：

BFS/DFS ，因为标签唯一，所以用Map保存对应关系，这里用dfs递归拷贝新节点。

算法：

Map<Integer, UndirectedGraphNode> sets = new HashMap<Integer, UndirectedGraphNode>();  
public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {  
    if(node == null)  
        return null;  
    if(sets.containsKey(node.label))  
        return sets.get(node.label);  
      
    UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);  
    sets.put(newNode.label, newNode);  
    for (UndirectedGraphNode neighbor : node.neighbors) {  
        newNode.neighbors.add(cloneGraph(neighbor));  
    }  
    return newNode;  
}