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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. vector<int> vec;
  5. int n;
  6.  
  7. int recur(int l, int r) {
  8.     int ans = 0;
  9.     if (l + 1 >= r) {
  10.         return ans;
  11.     }
  12.     int mid = (l + r) / 2;
  13.     ans += recur(l, mid);
  14.     ans += recur(mid, r);
  15.  
  16.     // Debugging output
  17.     cout << l << " " << r << endl;
  18.  
  19.     // Count inversions
  20.     int i = l, j = mid;
  21.     while (i < mid && j < r) {
  22.         if (vec[i] <= vec[j]) {
  23.             i++;
  24.         } else {
  25.             ans += mid - i;
  26.             j++;
  27.         }
  28.     }
  29.  
  30.     inplace_merge(vec.begin() + l, vec.begin() + mid, vec.begin() + r);
  31.     return ans;
  32. }
  33.  
  34. int main() {
  35.     cin >> n;
  36.     vec.resize(n);
  37.     for (int i = 0; i < n; i++) {
  38.         cin >> vec[i];
  39.     }
  40.     cout << recur(0, n) << endl;
  41. }
  42.  
Success #stdin #stdout 0s 5280KB
comments (?)
stdin
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10
1 5 6 9 8 7 10 2 4 3
stdout
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0 2
3 5
2 5
0 5
5 7
8 10
7 10
5 10
0 10
22
https://ideone.com/banGrT
language:
C++14 (gcc 8.3)
created:
5 days ago
visibility:
public

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