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

/ \

\_/

这道题不是很难，但是需要非常细心。用一个Queue来进行BFS，并用一个map来映射新node和旧node。对于每个旧node的邻居，新建一个与这个邻居相同的node，并把它加入与这个旧node对应的新node的neighbor list中。

/** * Definition for undirected graph. * class UndirectedGraphNode { * int label; * List<UndirectedGraphNode> neighbors; * UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */ public class Solution { public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) { if(node == null) return null; LinkedList<UndirectedGraphNode> q = new LinkedList<UndirectedGraphNode>(); HashMap<UndirectedGraphNode, UndirectedGraphNode> map = new HashMap<UndirectedGraphNode, UndirectedGraphNode>(); UndirectedGraphNode newNode = new UndirectedGraphNode(node.label); q.add(node); map.put(node, newNode); while(q.size() != 0){ UndirectedGraphNode cur = q.pop(); for(UndirectedGraphNode n: cur.neighbors){ if(!map.containsKey(n)){ UndirectedGraphNode copy = new UndirectedGraphNode(n.label); map.put(n, copy); map.get(cur).neighbors.add(copy); q.add(n); } else{ map.get(cur).neighbors.add(map.get(n)); } } } return newNode; } }