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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5.  
  6.     int n;int tg;
  7.     cin>>n;cin>>tg; 
  8.     vector <int> ar;
  9.     for(int i=0;i<=n-1;i++){
  10.     	int y;cin>>y; 
  11.     	ar.push_back(y); 
  12.     }
  13.  
  14.  
  15.     int ct = 0;
  16.     unordered_map<int, int> mp;
  17.  
  18.     for (int j = 0; j < n; j++) {
  19.         int df = tg - ar[j];
  20.  
  21.         if (mp.count(df)) {
  22.             ct += mp[df];
  23.         }
  24.  
  25.         mp[ar[j]]++;
  26.     }
  27.  
  28.     cout << ct << endl;
  29.  
  30.     return 0;
  31. }
Success #stdin #stdout 0s 5320KB
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https://ideone.com/KUTuoT
language:
C++14 (clang 8.0)
created:
14 hours ago
visibility:
public

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