inversions-PROP

#include <iostream>
#include <vector>
using namespace std;

void swap(vector<int>& V, int e, int d){
    int aux = V[e];
    V[e] = V[d];
    V[d] = aux;
}

int conta_inv(vector<int>& V, int e, int d){

    if (e>=d) return 0;
    else if (e == d-1){
        if (V[e] > V[d]) {
            swap(V, e, d);
            return 1;

        }
        else return 0;
    }
    else {

        int m = (e+d)/2;
        int inv_e = conta_inv(V, e, m);
        int inv_d = conta_inv(V, m+1, d);


        int cont = 0;

        vector<int> v1,v2;

        for (int x=e; x<=m; x++) v1.push_back(V[x]);
        for (int x=m+1; x<=d; x++) v2.push_back(V[x]);

        int i = 0;
        int j = 0;
        int k = e;
        while (i < v1.size() and j < v2.size()){
            if (v1[i] <= v2[j]){
                V[k] = v1[i];
                i++;
            }
            else {
                V[k] = v2[j];
                j++;
                cont += v1.size() - i;
            }
            k++;
        }
        while (i < v1.size()){
            V[k] = v1[i];
            i++; k++;
        }
        while (j < v2.size()){
            V[k] = v2[j];
            j++; k++;
        }

        return inv_e + inv_d + cont;
    }
}

int main(){
    int n;
    while (cin >> n) {
        vector<int> V(n);
        for (int i=0; i<n; i++) cin >> V[i];
        cout << conta_inv(V,0,n-1) << endl;
    }
}