[Leetcode] clone Graph

Clone an undirected graph. each node in the graph containslabelAnd a list of itsneighbors.

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#.

1. First node is labeled0. Connect Node0To both nodes1And2.
2. Second node is labeled1. Connect Node1To Node2.
3. Third node is labeled2. Connect Node2To Node2(Itself), thus forming a self-cycle.

 

Visually, the graph looks like the following:

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

Topic: clone a graph using the DFS recursive method, and use hashmap to save the ing between the nodes in the source image and those in the new graph. In addition, this hashmap can be used to determine whether a node has been cloned in O (1) time, and know the new node it has been cloned.

To implement a clone node method, in this method:

1. Determine whether the node has been cloned. If yes, return the corresponding clone node;
2. If the node has not been cloned, create a new node as the clone node of the node and recursively clone its neighbor node into the neighbors list of the node;

The Code is as follows:

 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 }