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
         / \
         \_/

[Notes]:
这道题是一个DFS， 借助queue做DFS遍历，借助hashmap记录那些copy的node已经建立过。

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode {
 *     int label;
 *     List neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList(); }
 * };
 */
public class Solution {
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        if(node==null) return null;
        //create a linkedlist for bfs
        LinkedList queue = new LinkedList();
        //create hashmap for clone
        HashMap map = new HashMap();
        queue.add(node);
        UndirectedGraphNode newHead = new UndirectedGraphNode(node.label);
        map.put(node, newHead);
        
        while(!queue.isEmpty()){
            UndirectedGraphNode cur = queue.remove();
            List curNeighbors = cur.neighbors;
            
            for(UndirectedGraphNode n : curNeighbors){
                if(map.containsKey(n))
                    map.get(cur).neighbors.add(map.get(n));//map中有n，则把n的copy加入到cur的copy的neighbor list里即可
                else{
                    queue.add(n);//map中没有，则queue中也没有。
                    UndirectedGraphNode newNode = new UndirectedGraphNode(n.label);
                    map.put(n, newNode);
                    map.get(cur).neighbors.add(newNode);
                }
            }
        }
        
        return newHead;
    }
}