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  1. #include <bits/stdc++.h>
  2. #define ll long long
  3. using namespace std;
  4. const ll N = 1e6 + 5;
  5. ll n, b, a[N];
  6. void Task() {
  7.     ios_base::sync_with_stdio(false);
  8.     cin.tie(0);
  9.     cout.tie(0);
  10.     if (fopen("FRIEND.inp", "r")) {
  11.         freopen("FRIEND.inp", "r", stdin);
  12.         freopen("FRIEND.out", "w", stdout);
  13.     }
  14. }
  15.  
  16. void Solve() {
  17.     cin >> n >> b;
  18.     for (int i = 1; i <= n; i++) cin >> a[i];
  19.     sort(a + 1, a + n + 1);
  20.     ll dem = 0;
  21.     for (int i = 1; i <= n; i++) {
  22.         ll j1 = lower_bound(a + 1, a + n + 1, b - a[i]) - a;
  23.         ll j2 = upper_bound(a + 1, a + n + 1, b - a[i]) - a - 1; 
  24.         if (b - a[i] < a[i]) {
  25.             dem += j2 - j1 + 1;
  26.         }
  27.     }
  28.     cout << dem << "\n";
  29. }
  30.  
  31. int main() {
  32.     Task();
  33.     Solve();
  34.     return 0;
  35. }
  36.  
Success #stdin #stdout 0.01s 5276KB
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https://ideone.com/pWeZ10
language:
C++ (gcc 8.3)
created:
34 days ago
visibility:
public

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