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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define int long long
  5. const int N = 6e5 + 5;
  6. int n , k;
  7. int a[N];
  8. map < int , int > cnt;
  9.  
  10.  
  11. main()
  12. {
  13.     ios::sync_with_stdio(0);
  14.     cin.tie(0);
  15.     cin >> n >> k;
  16.     for(int i = 1 ; i <= n ; i++)
  17.         cin >> a[i];
  18.     /// x3 < x4
  19.     int ans = 0;
  20.     for(int x3 = 1 ; x3 <= n ; x3++)
  21.     {
  22.         for(int x4 = x3 + 1 ; x4 <= n ; x4++)
  23.             ans += cnt[a[x3] + a[x4] + (int)3e5];
  24.  
  25.         /// x1 < x2 = x3
  26.         for(int x1 = 1 ; x1 <= x3 - 1 ; x1++)
  27.             cnt[k - a[x1] - a[x3] + (int)3e5]++;
  28.     }
  29.     cout << ans << "\n";
  30.  
  31.  
  32. }
Success #stdin #stdout 0.01s 5296KB
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stdin 
Standard input is empty
stdout 
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https://ideone.com/WoYT2O
language:
C++14 (gcc 8.3)
created:
24 days ago
visibility:
public

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