Countinversions

#include<bits/stdc++.h>
using namespace std;
 
int getSum(int BITree[], int index)
{
    int sum = 0; // Initialize result
 
    while (index > 0)
    {
        sum += BITree[index];
        index -= index & (-index);
    }
    return sum;
}
 
void updateBIT(int BITree[], int n, int index, int val)
{
    while (index <= n)
    {
       BITree[index] += val;
       index += index & (-index);
    }
}
 
int getInvCount(int arr[], int n)
{
    int invcount = 0; 
    int maxElement = 0;
    for (int i=0; i<n; i++)
        if (maxElement < arr[i])
            maxElement = arr[i];
 
    int BIT[maxElement+1];
    for (int i=1; i<=maxElement; i++)
        BIT[i] = 0;
 
    for (int i=n-1; i>=0; i--)
    {
        invcount += getSum(BIT, arr[i]-1);
 
        updateBIT(BIT, maxElement, arr[i], 1);
    }
 
    return invcount;
}
 
int main()
{
    int arr[] = {8, 4, 2, 1};
    int n = sizeof(arr)/sizeof(int);
    cout << "Number of inversions are : " << getInvCount(arr,n);
    return 0;
}