Inversion of array

#include <bits/stdc++.h>
using namespace std;
 
long long _mergeSort(long long arr[], long long temp[], long long left, long long right);
long long merge(long long arr[], long long temp[], long long left, long long mid, long long right);

long long mergeSort(long long arr[], long long array_size)
{
    long long temp[array_size];
    return _mergeSort(arr, temp, 0, array_size - 1);
}

long long _mergeSort(long long arr[], long long temp[],long long left, long long right){
    long long 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;
}
long long merge(long long arr[], long long temp[], long long left,long long mid, long long right){
    long long i, j, k;
    long long inv_count = 0;
    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++];
            inv_count = inv_count + (mid - i);
        }
    }
     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 t;
    scanf("%d",&t);
    while(t--){
        long long n,count=0;
        cin >> n;
        long long arr[n];
        for(long long i=0;i<n;i++) cin >> arr[i];
        long long ans = mergeSort(arr, n);
        cout << ans << endl;
    }
    return 0;
}