LeetCode题解：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
     / \
     \_/

题意：想办法用这种方式表示一张无向图：{0,1,2#1,2#2,2}，表示该图有3个结点，#号为每个节点的划分符，0，1，2表示0为起点，能到达的点是1和2；1，2代表1为起点，2为终点。

代码：

/** * Definition for undirected graph. * class UndirectedGraphNode { * int label; * List<UndirectedGraphNode> neighbors; * UndirectedGraphNode(int x) { label = x; neighbors = new ArrayList<UndirectedGraphNode>(); } * }; */
public class Solution {
    private HashMap<Integer, UndirectedGraphNode> map = new HashMap<>();

    public UndirectedGraphNode cloneGraph(UndirectedGraphNode node) {
        return clone(node);
    }

    private UndirectedGraphNode clone(UndirectedGraphNode node){
        if(node == null){
            return null;
        }

        if(map.containsKey(node.label)){
            return map.get(node.label);
        }

        UndirectedGraphNode temp = new UndirectedGraphNode(node.label);
        map.put(temp.label, temp);
        for(UndirectedGraphNode neighbor : node.neighbors){
            temp.neighbors.add(clone(neighbor));
        }

        return temp;
    }
}