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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 d;
  16.     cin >> d;
  17.  unordered_map<ll, ll> mp;
  18.  
  19.     ll counter = 0;
  20.  
  21.    for(int i=0;i<n; i++){
  22.    	ll real = A[i]%d;
  23.  
  24.    	ll r = d- real;
  25.  
  26.    	r= r%d;
  27.    	counter+=mp[r];
  28.  
  29.    	for (int j=0;j<i;j++){
  30.    		ll sum = A[i]+A[j];
  31.    		sum= sum%d;
  32.    		mp[sum]++;
  33.    	}
  34.    }
  35.    cout<<counter<<endl;
  36.  
  37.     return 0;
  38. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/EmI35D
language:
C++ (gcc 8.3)
created:
12 hours ago
visibility:
public

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