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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. long long d[16];
  4. int main()
  5. {
  6.     ios_base::sync_with_stdio(false);
  7.     cin.tie(0);
  8.     if (fopen("cpair11.inp", "r"))
  9.     {
  10.         freopen("cpair11.inp", "r", stdin);
  11.         freopen("cpair11.out", "w", stdout);
  12.     }
  13.     int n;
  14.     cin >> n;
  15.     for (int i=1; i<=n; i++)
  16.     {
  17.         int a;
  18.         cin >> a;
  19.         d[(a*a)%11]++;
  20.     }
  21.     cout << d[0]*(d[0]-1)/2+d[1]*(d[1]-1)/2+d[3]*(d[3]-1)/2+d[4]*(d[4]-1)/2+d[5]*(d[5]-1)/2+d[9]*(d[9]-1)/2;
  22. }
  23.  
Success #stdin #stdout 0s 5320KB
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https://ideone.com/yIlcqs
language:
C++14 (gcc 8.3)
created:
22 hours ago
visibility:
public

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