Nodes are labeled uniquely.

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 #.

1. First node is labeled as 0. Connect node 0 to both nodes 1 and 2.
2. Second node is labeled as 1. Connect node 1 to node 2.
3. 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         /          \_/

 1 /** 2  * Definition for undirected graph. 3  * struct UndirectedGraphNode { 4  *     int label; 5  *     vector<UndirectedGraphNode *> neighbors; 6  *     UndirectedGraphNode(int x) : label(x) {}; 7  * }; 8  */ 9 class Solution {10 public:11     void cloneNode(UndirectedGraphNode *&res, UndirectedGraphNode *node, map<int, UndirectedGraphNode*> &mp) {12         if (mp[node->label] != NULL) {13             res = mp[node->label];14             return;15         }16         res = new UndirectedGraphNode(node->label);17         res->neighbors.resize(node->neighbors.size());18         mp[node->label] = res;19 20         for (int i = 0; i < node->neighbors.size(); ++i) {21             cloneNode(res->neighbors[i], node->neighbors[i], mp);22         }23     }24     25     UndirectedGraphNode *cloneGraph(UndirectedGraphNode *node) {26         if (node == NULL) return NULL;27         map<int, UndirectedGraphNode*> mp;28         UndirectedGraphNode* res; 29         cloneNode(res, node, mp);30         return res;31     }32 };