变量unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> cloneMap;

因为会有环，所以需要cloneMap记录旧的节点和新的节点对。

还需要一个visited记录已经访问过的节点，可以和cloneMap合并在一起。

DFS：

在克隆某个Node时，首先放入map中。

之后遍历neighbors。如果neighbors不在map里，即没有访问过，则递归调用cloneGraph函数。

最后返回克隆过的节点。

    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == NULL) return NULL;
        if (cloneMap.find(node) != cloneMap.end()) 
            return cloneMap[node];
        cloneMap[node] = new UndirectedGraphNode(node->label);
        cloneMap[node]->neighbors = vector<UndirectedGraphNode *>();
        for (int i = 0; i < node->neighbors.size(); i++)
        {
            UndirectedGraphNode * curNode = node->neighbors[i];
            UndirectedGraphNode * newNode = cloneGraph(curNode);
            cloneMap[node]->neighbors.push_back(newNode);
        }
        return cloneMap[node];
    }

BFS：

使用一个queue记录要访问的节点。

因为不能在访问queue中节点的时候再创建对应的node==>因为在处理父亲节点的时候需同时创建好其neighbors

所以需要在将不在map中的neighbors（没有访问过的子节点）放入queue的同时创建克隆的节点，并且放入map里。

    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {
        if (node == NULL) return NULL;
        vector<UndirectedGraphNode *> queue;
        queue.push_back(node);
        cloneMap[node] = new UndirectedGraphNode(node->label);
        cloneMap[node]->neighbors = vector<UndirectedGraphNode *>();
        
        for (int i = 0; i < queue.size(); i++)
        {
            UndirectedGraphNode * newNode = cloneMap[queue[i]];
            for (int j = 0; j < queue[i]->neighbors.size(); j++)
            {
                UndirectedGraphNode * curNb = queue[i]->neighbors[j];
                if (cloneMap.find(curNb) == cloneMap.end())
                {
                    queue.push_back(curNb);
                    UndirectedGraphNode * newNb = new UndirectedGraphNode(curNb->label);
                    newNb->neighbors = vector<UndirectedGraphNode *>();
                    cloneMap[curNb] = newNb;
                }
                newNode->neighbors.push_back(cloneMap[curNb]);
            }
        }
        return cloneMap[node];
    }

Clone Graph [leetcode] dfs和bfs