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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. typedef long long int ll;
  5.  
  6. int main() {
  7.     int n;
  8.     cin >> n;
  9.  
  10.     vector<ll> A(n);
  11.     for (int i = 0; i < n; i++) {
  12.         cin >> A[i];
  13.     }
  14.  
  15.     ll k;
  16.     cin >> k;
  17.  
  18.     ll counter = 0;
  19.  
  20.     unordered_map<ll, ll> mp;
  21.  
  22.  for(int j= 0;j<n; j++ ){
  23.  	 ll real = A[j]%k ;
  24.  	  ll r= k- real;
  25.  
  26.  	  r= r%k;
  27.  
  28.  	  counter+= mp[r];
  29.  
  30.  	  mp[A[j]%k]++;
  31.  }
  32.  cout<<counter<<endl;
  33.  
  34.     return 0;
  35. }
  36.  
Success #stdin #stdout 0s 5328KB
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https://ideone.com/BNMBQc
language:
C++ (gcc 8.3)
created:
13 hours ago
visibility:
public

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