Leetcode: 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
     /      \_/

题目要求克隆图，采用深度优先或者广度优先进行遍历。使用一个Map存储原始节点和克隆以后的节点。

参考代码（使用深度优先遍历）：

/**
 * Definition for undirected graph.
 * struct UndirectedGraphNode {
 *     int label;
 *     vector<UndirectedGraphNode*> neighbors;
 *     UndirectedGraphNode(int x) : label(x) {};
 * };
 */
class Solution 
{
public:
    UndirectedGraphNode* cloneGraph(UndirectedGraphNode* node) 
    {
        if (node == nullptr)    return nullptr;

        // map的key为原始节点，value为拷贝的节点
        unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> copyMap;
        // 完成给定节点的图的拷贝工作
        clone(node, copyMap);

        return copyMap[node];
    }
private:
    static UndirectedGraphNode* clone(UndirectedGraphNode* node, unordered_map<UndirectedGraphNode*, UndirectedGraphNode*> &copyMap)
    {
        // 如果该节点已经拷贝过，直接返回该节点的拷贝
        if (copyMap.find(node) != copyMap.end())  return copyMap[node];

        // 否则，拷贝该节点及其相邻节点
        UndirectedGraphNode* copiedNode = new UndirectedGraphNode(node->label);
        copyMap[node] = copiedNode;
        for (auto neighborNode : node->neighbors)
            copiedNode->neighbors.push_back(clone(neighborNode, copyMap));

        return copiedNode;
    }
};