UVA-1595 Symmetry

 1 #include <stdio.h>
 2 #include <iostream>
 3 #include <algorithm>
 4 #include <set>
 5 
 6 using namespace std;
 7 
 8 int main ()
 9 {
10     int N;
11     cin >> N;
12     while(N --)
13     {
14         int M;
15         cin >> M;
16         int tmp_M = M;
17         set<pair<int,int>> s;
18         double m = 0;
19         while(tmp_M --)
20         {
21             int a,b;
22             cin >> a >> b;
23             m += a;
24             s.insert(make_pair(a,b));
25         }
26     //    cout << m << endl;
27         m /= M;
28         
29         int flag = 1;
30         for(auto Ptr = s.begin();Ptr!=s.end();Ptr++)
31         {
32             int a = 2*m-Ptr->first;
33             int b = Ptr->second;
34             if(!s.count(make_pair(a,b)))
35             {
36                 flag =  0;
37                 break;
38             }
39         }
40         if(flag)
41             cout << "YES" << endl;
42         else
43             cout << "NO" << endl;
44     }
45     return 0;
46 }