直接计算逆序对

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

int countInversions(vector<int>& arr) {
    int inversions = 0;
    for (int i = 0; i < arr.size(); ++i) {
        for (int j = i + 1; j < arr.size(); ++j) {
            if (arr[i] > arr[j]) {
                ++inversions;
            }
        }
    }
    return inversions;
}

int main() {
    int T;
    cin >> T;

    while (T--) {
        int n;
        cin >> n;
        vector<int> arr(n);

        for (int i = 0; i < n; ++i) {
            cin >> arr[i];
        }
        int swaps = countInversions(arr);

        cout << "Optimal train swapping takes " << swaps << " swaps." << endl;
    }

    return 0;
}