class Solution {private:    unordered_map<UndirectedGraphNode *, UndirectedGraphNode *> umap;public:// 用DFS// 用map来存储，key是旧的结点地址，value是新的结点地址// 第一遍，如果没有访问过，就clone并加入umap// 第二遍，如果没有访问过，就clone他的neighbors    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        if(node == NULL) return NULL;        DFS(node);        DFSNei(node);        return umap[node];           }    void DFS(UndirectedGraphNode *node){        umap[node] = new UndirectedGraphNode(node->label); // 访问node        for(auto nei: node->neighbors){ // 访问与Node相邻的            if(umap.count(nei) == 0){ // 如果没有访问过                DFS(nei);            }        }    }    void DFSNei(UndirectedGraphNode *node){        for(auto nei: node->neighbors){ // clone umap[node]的neighbors            umap[node]->neighbors.push_back(umap[nei]);        }        for(auto nei: node->neighbors){            if(!nei->neighbors.empty() && umap[nei]->neighbors.empty()){               DFSNei(nei);            }        }    }};