Can anybody tell me how to do count number of inversions with quick sort?

import java.util.ArrayList;

import java.util.Collections;

public class Quicksort {

int inversioncount = 0;

public int partition(ArrayList arr, int low, int high)

{

int pivot = arr.get(high);

int i = (low-1); // index of smaller element

for (int j=low; j

{

// If current element is smaller than or

// equal to pivot

if (arr.get(j) <= pivot)

{

i++;

//swap elements

Collections.swap(arr, i, j);

}

}

//swap elements

Collections.swap(arr, i+1, high);

return i+1;

}

//ArrayList arr --> Array to be sorted,

//low --> Starting index,

//high --> Ending index

public int sort(ArrayList arr, int low, int high)

{

if (low < high)

{

/* pi is partitioning index, arr[pi] is

now at right place */

int pi = partition(arr, low, high);

// Recursively sort elements before

// partition and after partition

sort(arr, low, pi-1);

sort(arr, pi+1, high);

}

return inversioncount;

}

}