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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. #define int long long
  5. // #define ll long long
  6.  
  7. mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
  8.  
  9. int rand(int L, int R) {
  10.     return uniform_int_distribution<int>(L, R)(rng);
  11. }
  12.  
  13. const int N = 100000+5;
  14. int bit[N], a[N];
  15. int n; 
  16.  
  17. void update(int x) {
  18.     while (x < N) {
  19.         bit[x]++; 
  20.         x += (x & (-x));
  21.     }
  22. }
  23.  
  24. int get(int x) {
  25.     int res = 0;
  26.     while (x > 0) {
  27.         res += bit[x]; 
  28.         x -= (x & (-x));
  29.     }
  30.     return res;
  31. }
  32.  
  33. void solve() {
  34.     cin >> n; 
  35.     for (int i = 1; i <= n; i++) cin >> a[i];
  36. 	int answer = 0; 
  37. 	for (int i = n; i >= 1; i--) {
  38. 		answer += get(a[i]-1); 
  39. 		update(a[i]); 
  40. 	}
  41. 	cout << answer << '\n';
  42. }
  43.  
  44. signed main() {
  45.     ios_base::sync_with_stdio(false);
  46.     cin.tie(0);
  47.     // int t; cin >> t;
  48.     // while (t--) solve();
  49.     solve();
  50. }
Success #stdin #stdout 0.01s 5280KB
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https://ideone.com/vUuuEt
language:
C++14 (gcc 8.3)
created:
12 days ago
visibility:
public

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