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【leetcode】Clone Graph

2024-07-12 21:09:37   228人阅读

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         /          \_/

题解：利用DFS递归的方法克隆图，用hashmap保存原图中的节点和新图中的节点的对应关系。而且利用这个hashmap可以在O(1)的时间内判断一个节点是否被克隆过，并且知道克隆它得到的新节点。

实现一个克隆节点的方法，在这个方法中：

  1. 判断这个节点是否被clone过了，如果是，返回它对应的clone节点；
  2. 如果没有被clone过，那么新建节点为该节点的clone节点，并且递归的clone它的邻居节点，放入该节点的neighbors列表里面；

代码如下：

 1 /** 2  * Definition for undirected graph. 3  * class UndirectedGraphNode { 4  *     int label; 5  *     List<UndirectedGraphNode> neighbors; 6  *     UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } 7  * }; 8  */ 9 public class Solution {10     private HashMap<UndirectedGraphNode,UndirectedGraphNode> mapClone = new HashMap<UndirectedGraphNode,UndirectedGraphNode>();11     12     private UndirectedGraphNode cloneNode(UndirectedGraphNode node){13         if(node == null)14             return null;15         //if this node already has a clone16         if(mapClone.containsKey(node))17             return mapClone.get(node);18         19         //if this node hasn‘t been cloned, we construct a new node copy20         UndirectedGraphNode copy = new UndirectedGraphNode(node.label);21         mapClone.put(node, copy);22         23         //clone all the neighbers of node24         for(UndirectedGraphNode n:node.neighbors){25             copy.neighbors.add(cloneNode(n));26         }27         return copy;28     }29     public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {30         return cloneNode(node);31     }32 }

 


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