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
         / 
         \_/
这道题题目有点长，略微有点烦。这道题思路还是比较简单，直接用DFS或者BFS可以A
这里我用的是DFS
ps：剩下leetcode上面的hard类型了

import java.util.ArrayList;

import java.util.Hashtable;
import java.util.List;

public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(null == node)
            return node;
        boolean isFirst = true;
        Hashtable<UndirectedGraphNode, Integer> visited = new Hashtable<UndirectedGraphNode, Integer>();
        Hashtable<UndirectedGraphNode, UndirectedGraphNode> map = new Hashtable<UndirectedGraphNode, UndirectedGraphNode>();
        
        DFS(node, visited, map, isFirst);
        
        visited = new Hashtable<UndirectedGraphNode, Integer>();
        isFirst = false;
        DFS(node, visited, map, isFirst);
        
        return map.get(node);
        
    }
    
    private void DFS(UndirectedGraphNode node, Hashtable<UndirectedGraphNode, Integer> visited, 
            Hashtable<UndirectedGraphNode, UndirectedGraphNode> map, boolean isFirst){
        if(visited.get(node) == null){            
            if(isFirst){
                UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
                map.put(node, newNode);                                                    //key为旧的引用，value为新的引用
            }
            
            //深度遍历
            List<UndirectedGraphNode> neighborsList = node.neighbors;
            visited.put(node, 1);                                                    //标记为已访问
            for(UndirectedGraphNode nodeInList : neighborsList){
                if(isFirst){                                                        //第一次遍历
                    DFS(nodeInList, visited, map, isFirst);
                }else{                                                                //第二次遍历
                    if(map.get(node).neighbors == null)
                        map.get(node).neighbors = new ArrayList<UndirectedGraphNode>();
                    map.get(node).neighbors.add(map.get(nodeInList));
                    DFS(nodeInList, visited, map, isFirst);
                }
            }
        }
        else
            return;
    }
}