void mergeSort(int arr[], int l, int r)
{
if(l < r)
{
int m = (l+r)/2;
mergeSort(arr, l, m);
mergeSort(arr, m+1, r);
mergeAndCount(arr, l, m, r);
}
}
public static int countInversions(int nums[])
{
int mid = nums.length/2, k;
int countLeft, countRight, countMerge;
if (nums.length <= 1)
return 0;
int left[] = new int[mid];
int right[] = new int[nums.length - mid];
for (k = 0; k < mid; k++)
left[k] = nums[k];
for (k = 0; k < nums.length - mid; k++)
right[k] = nums[mid+k];
countLeft = countInversions (left);
countRight = countInversions (right);
int result[] = new int[nums.length];
countMerge = mergeAndCount (left, right, result);
for (k = 0; k < nums.length; k++)
nums[k] = result[k];
return (countLeft + countRight + countMerge);
}