#include <bits/stdc++.h>
using
namespace
std;
int
_mergeSort(
int
arr[],
int
temp[],
int
left,
int
right);
int
merge(
int
arr[],
int
temp[],
int
left,
int
mid,
int
right);
int
mergeSort(
int
arr[],
int
array_size)
{
int
temp[array_size];
return
_mergeSort(arr, temp, 0, array_size - 1);
}
int
_mergeSort(
int
arr[],
int
temp[],
int
left,
int
right)
{
int
mid, inv_count = 0;
if
(right > left) {
mid = (right + left) / 2;
inv_count = _mergeSort(arr, temp, left, mid);
inv_count += _mergeSort(arr, temp, mid + 1, right);
inv_count += merge(arr, temp, left, mid + 1, right);
}
return
inv_count;
}
int
merge(
int
arr[],
int
temp[],
int
left,
int
mid,
int
right)
{
int
i, j, k;
int
inv_count = 0;
i = left;
j = mid;
k = left;
while
((i <= mid - 1) && (j <= right)) {
if
(arr[i] > 2 * arr[j]) {
inv_count += (mid - i);
j++;
}
else
{
i++;
}
}
i = left;
j = mid;
k = left;
while
((i <= mid - 1) && (j <= right)) {
if
(arr[i] <= arr[j]) {
temp[k++] = arr[i++];
}
else
{
temp[k++] = arr[j++];
}
}
while
(i <= mid - 1)
temp[k++] = arr[i++];
while
(j <= right)
temp[k++] = arr[j++];
for
(i = left; i <= right; i++)
arr[i] = temp[i];
return
inv_count;
}
int
main()
{
int
arr[] = { 1, 20, 6, 4, 5 };
int
n =
sizeof
(arr) /
sizeof
(arr[0]);
cout << mergeSort(arr, n);
return
0;
}