Clone Graph

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     / \     \_/

哈希表法

复杂度

时间 O(N) 空间 O(N)

思路

广度优先搜索，同时用一个哈希表，将新旧节点映射起来。这样我们第一次遍历到的节点，我们会新建一个节点并映射到哈希表中。当以后再遍历到这个节点时，我们可以直接用哈希表取出它对应的新节点。

代码

public class Solution {    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {        if(node == null) return null;        Queue<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>();        Map<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>();        UndirectedGraphNode root = new UndirectedGraphNode(node.label);        map.put(node, root);        q.offer(node);        while(!q.isEmpty()){UndirectedGraphNode curr = q.poll();// 将curr旧节点的邻居节点都加入curr的新节点for(UndirectedGraphNode oldNeighbor : curr.neighbors){    // 判断是否已经生成过该邻居节点的新节点    UndirectedGraphNode newNeighbor = map.get(oldNeighbor);    if(newNeighbor == null){        newNeighbor = new UndirectedGraphNode(oldNeighbor.label);        // 如果是第一次生成该新节点，将其加入队列中        q.offer(oldNeighbor);        map.put(oldNeighbor, newNeighbor);    }    // 将新邻居加入新curr节点的neighbors中    map.get(curr).neighbors.add(newNeighbor);}        }        return root;    }}