133. Clone Graph-优快云博客

本文介绍了一种使用递归和哈希映射实现无向图的深拷贝方法，确保了图中每个节点及其邻居被正确复制，即使存在自环也能妥善处理。

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:

深拷贝一个图，图可能有自环。

图中顶点的编号是unique的，利用这一点，可以在递归调用中识别已经copy的节点。

 HashMap<UndirectedGraphNode, Boolean> hashmap=new HashMap<>();
	HashMap<Integer, UndirectedGraphNode> newhashmap=new HashMap<>();
	
	public UndirectedGraphNode cloneGraph(UndirectedGraphNode node)
	{
		if(node==null)
			return node;
		
		hashmap.put(node, true);
		UndirectedGraphNode newnode=new UndirectedGraphNode(node.label);
		newhashmap.put(newnode.label,newnode);
		
		for(UndirectedGraphNode tn : node.neighbors)
		{
			if(!hashmap.containsKey(tn))
				{
					hashmap.put(tn, true);
					UndirectedGraphNode temp=cloneGraph(tn);
					newnode.neighbors.add(temp);
				}
			else
			{
				int lable=tn.label;
				newnode.neighbors.add(newhashmap.get(lable));
			}
		}
		
		return newnode;
	}