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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 target;
  16.     cin >> target;
  17.  
  18.     ll count =0;
  19.  
  20.    unordered_map<ll, ll> mpp;
  21.  
  22.    for(int j=0;j<n ;j++){
  23.    	ll r1= target - A[j];
  24.    	ll r2= -1*target - A[j];
  25.  
  26.    	if(target==0)
  27.    	count+=mpp[r1];
  28.  
  29.    	else{
  30.    		count+= mpp[r1];
  31.    		count+= mpp[r2];
  32.    	}
  33.  
  34.    	mpp[A[j]]++;
  35.  
  36.    }
  37.    cout<<count<<endl;
  38.  
  39.     return 0;
  40. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/JhPUkq
language:
C++ (gcc 8.3)
created:
16 hours ago
visibility:
public

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