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  1. #include <bits/stdc++.h>
  2.  
  3. typedef long long ll;
  4.  
  5. using namespace std;
  6.  
  7. ll n, x, a[40];
  8. vector<ll> le, ri;
  9.  
  10. vector<ll> f(int l, int r) {
  11.     int m = r - l + 1;
  12.     vector<ll> res;
  13.     for (int i = 0; i < (1 << m); i++) {
  14.         ll sum = 0;
  15.         for (int j = 0; j < m; j++) {
  16.             if (i & (1 << j)) {
  17.                 sum += a[l + j];
  18.             }
  19.         }
  20.         res.push_back(sum);
  21.     }
  22.     return res;
  23. }
  24.  
  25.  
  26. int main() {
  27.     cin.tie(0) -> sync_with_stdio(false), cout.tie(0);
  28.     cin >> n >> x;
  29.     for (int i = 0; i < n; i++) {
  30.         cin >> a[i];
  31.     }
  32.     le = f(0, n / 2 - 1), ri = f(n / 2, n - 1);
  33.     sort(le.begin(), le.end()), sort(ri.begin(), ri.end());
  34.     ll ans = 0;
  35.     for (auto i : le) {
  36.         auto lo = lower_bound(ri.begin(), ri.end(), x - i);
  37.         auto hi = upper_bound(ri.begin(), ri.end(), x - i);
  38.         ans += hi - lo;
  39.     }
  40.     cout << ans << '\n';
  41.     return 0;
  42. }
Success #stdin #stdout 0.01s 5292KB
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https://ideone.com/zq7orS
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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