Given nums1 = [1, 2, 2, 1], nums2 = [2, 2], return [2].

 1 class Solution {
 2 public:
 3     vector<int> intersection(vector<int>& nums1, vector<int>& nums2) 
 4     {
 5         std::vector<int> tVec;
 6         if (nums1.empty() || nums2.empty())
 7         {
 8             return tVec;
 9         }
10         std::set<int> tSet;
11         std::set<int> tResultSet;
12         for (int i=0; i<nums1.size(); i++)
13         {
14             tSet.insert(nums1.at(i));
15         }
16         for (int i=0; i<nums2.size(); i++)
17         {
18             if (tSet.find(nums2.at(i)) != tSet.end())
19             {
20                 tResultSet.insert(nums2.at(i));
21             }
22         }
23         std::set<int>::iterator it; 
24         for(it = tResultSet.begin(); it != tResultSet.end(); it++)  
25         {  
26             tVec.push_back(*it); 
27         }  
28         return tVec;        
29     }
30 };