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  1. #include <iostream>
  2. #include <vector>
  3. using namespace std;
  4.  
  5. // Hàm đếm số nghịch thế theo giải pháp O(n^2)
  6. int countInversionsNaive(const vector<int>& arr) {
  7.     int n = arr.size();
  8.     int count = 0;
  9.     for (int i = 0; i < n - 1; i++) {
  10.         for (int j = i + 1; j < n; j++) {
  11.             if (arr[i] > arr[j]) {
  12.                 count++;
  13.             }
  14.         }
  15.     }
  16.     return count;
  17. }
  18.  
  19. int main() {
  20.     int n;
  21.     cin >> n;
  22.     vector<int> arr(n);
  23.     for (int i = 0; i < n; i++) {
  24.         cin >> arr[i];
  25.     }
  26.     cout << "Number of inversions (O(n^2)): " << countInversionsNaive(arr) << endl;
  27.     return 0;
  28. }
Success #stdin #stdout 0.01s 5292KB
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stdin
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6
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stdout
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Number of inversions (O(n^2)): 5
https://ideone.com/vVZTgn
language:
C++14 (gcc 8.3)
created:
9 days ago
visibility:
public

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