码迷,mamicode.com
首页 > 编程语言 > 详细

[LeetCode][Java] Clone Graph

时间:2015-08-01 19:06:59      阅读:150      评论:0      收藏:0      [点我收藏+]

标签:leetcode   java   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
         /          \_/

题意:

克隆无向图。图中的每一个节点包含一个label 和 一组neighbors.

本题中的无向图的定义为:

每个节点都是唯一标记的。

我们通过#来划分每一个节点 通过,来划分节点标记和节点的每一个邻居。

举个例子,给定一个图{0,1,2#1,2#2,2}.

这个图中共3个节点,因此包含了通过#划分的三个部分.

   1.第一个节点被标记为 0.连接节点0和节点1 and 2.

   2.第二个节点被标记为 1.将节点1和 节点2相连接.

  3.第三个节点被标记为 2. 将节点2和节点2(它自身)想连接,这样就形成了自环.

这个图就如下面所示:

       1
      /      /       0 --- 2
         /          \_/

算法分析:


 * 共两种方法,DFS--递归, BFS--队列
  
 * 拷贝方法是用用HashMap,key存原始值,value存copy的值,用DFS或者BFS方法遍历帮助拷贝neighbors的值。
   
 * 但这里有个问题,在clone一个节点时我们需要clone它的neighbors,而邻居节点有的已经存在,有的未存在,如何进行区分?


 * 这里我们使用Map来进行区分,Map的key值为原来的node,value为新clone的node,当发现一个node未在map中时说明这个node还未被clone,


AC代码:

/**
 * Definition for undirected graph.
 * class UndirectedGraphNode 
 * {
 *     int label;
 *     List<UndirectedGraphNode> neighbors;
 *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); }
 * };
 */


方法一:广度优先搜索BFS 利用队列

public class Solution 
{
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node)
    {
        if(node == null)
            return null;
            
        HashMap<UndirectedGraphNode, UndirectedGraphNode> hm = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
        LinkedList<UndirectedGraphNode> queue = new LinkedList<UndirectedGraphNode>();
        UndirectedGraphNode head = new UndirectedGraphNode(node.label);
        hm.put(node, head);//key存原始值,value存copy的值
        queue.add(node);
        
        while(!queue.isEmpty())
        {
            UndirectedGraphNode curnode = queue.poll();
            for(UndirectedGraphNode aneighbor: curnode.neighbors)//check each neighbor
            {
                if(!hm.containsKey(aneighbor))//if not visited,then add to queue
                {
                    queue.add(aneighbor);
                    UndirectedGraphNode newneighbor = new UndirectedGraphNode(aneighbor.label);
                    hm.put(aneighbor, newneighbor);
                }
                hm.get(curnode).neighbors.add(hm.get(aneighbor));//head.neighbors.add(newneightbor)
            }
        }
        return head;
    }
}

方法二:通过递归进行DFS深度优先遍历

public class Solution 
{
    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) 
    {
            if(node == null)
                return null;
                
            HashMap<UndirectedGraphNode, UndirectedGraphNode> hm = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();
            UndirectedGraphNode head = new UndirectedGraphNode(node.label);//初始化话节点时没有邻接节点
            hm.put(node, head);//key存原始值,value存copy的值
            
            DFS(hm, node);//DFS
            return head;
    }
    public void DFS(HashMap<UndirectedGraphNode, UndirectedGraphNode> hm, UndirectedGraphNode node)
    {
        if(node == null)
            return;
            
        for(UndirectedGraphNode aneighbor: node.neighbors)
        { 
            if(!hm.containsKey(aneighbor))
            {
                UndirectedGraphNode newneighbor = new UndirectedGraphNode(aneighbor.label);
                hm.put(aneighbor, newneighbor);
                DFS(hm, aneighbor);//DFS
            }
            hm.get(node).neighbors.add(hm.get(aneighbor));//对该节点拷贝neighbors的值。
        }
    }
}

版权声明:本文为博主原创文章,转载注明出处

[LeetCode][Java] Clone Graph

标签:leetcode   java   clone graph   

原文地址:http://blog.csdn.net/evan123mg/article/details/47187775

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!