https://oj.leetcode.com/problems/clone-graph/

克隆一个可能有环的无向图。递归的重构出每个顶点即可。虽然有环，但是每个结点的label提供了该结点的唯一标示。可以使用一个map记录该标识下结点的地址。

/** * Definition for undirected graph. * struct UndirectedGraphNode { *     int label; *     vector
     
       neighbors; *     UndirectedGraphNode(int x) : label(x) {}; * }; */typedef UndirectedGraphNode scnode;class Solution {public:    map
      
        cm;    UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {        if (node==NULL) return NULL;        int cl=node->label;        if (cm.find(cl)!=cm.end()) return cm[cl];        scnode *cur=new scnode(cl);        cm[cl]=cur;        vector 
       
         &neis=node->neighbors;        for (int i=0;i
        
         neighbors.push_back(cloneGraph(p));        }        return cur;    }};