leetcode 133. Clone Graph 图遍历BFS + 避免循环-蒲公英云

leetcode 133. Clone Graph 图遍历BFS + 避免循环

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 #.

First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
Second node is labeled as 1. Connect node 1 to node 2.
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
     / \
     \_/

这道题考查的是图的遍历，可以使用BFS或者DFS，不过要避免循环。

代码如下：

import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;
/*class UndirectedGraphNode 
{
      int label;
      List<UndirectedGraphNode> neighbors;
      UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
};
*/
 /*
  * 这个题主要的注意就是使用map映射结点信息
  * */
public class Solution 
{
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) 
    {
        if(node==null)
            return null;
        UndirectedGraphNode newNode = new UndirectedGraphNode(node.label);
        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        map.put(node, newNode);
        Queue<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        queue.add(node);
        while(queue.isEmpty()==false)
        {
            UndirectedGraphNode top = queue.poll();
            List<UndirectedGraphNode> list = top.neighbors;
            for(int i=0;i<list.size();i++)
            {
                UndirectedGraphNode one = list.get(i);
                if(map.containsKey(one)==false)
                {
                    UndirectedGraphNode tmp = new UndirectedGraphNode(one.label);
                    map.put(one, tmp);
                    //只有新建的需要加入queue，否者不需要，避免图中的环
                    queue.add(one);
                }
                map.get(top).neighbors.add(map.get(one));
            }
        }
        return newNode;
    }
}