test.cpp

#include "test.h"
// Merges two subarrays of arr[]. 
// First subarray is arr[l..m] 
// Second subarray is arr[m+1..r] 
void merge(int arr[], int l, int m, int r, int* count) 
{ 
    int i, j, k; 
    int n1 = m - l + 1; 
    int n2 =  r - m; 
  
    /* create temp arrays */
    int *L = new int [n1];
    int *R = new int [n2];
        
  
    /* Copy data to temp arrays L[] and R[] */
    for (i = 0; i < n1; i++) 
        L[i] = arr[l + i]; 
    for (j = 0; j < n2; j++) 
        R[j] = arr[m + 1+ j]; 
  
    /* Merge the temp arrays back into arr[l..r]*/
    i = 0; // Initial index of first subarray 
    j = 0; // Initial index of second subarray 
    k = l; // Initial index of merged subarray 
    while (i < n1 && j < n2) 
    { 
        if (L[i] <= R[j]) 
        { 
            arr[k] = L[i]; 
            i++;
            *count++; 
        } 
        else
        { 
            arr[k] = R[j]; 
            j++; 
            *count++;
        } 
        k++;
    } 
  
    /* Copy the remaining elements of L[], if there 
       are any */
    while (i < n1) 
    { 
        arr[k] = L[i]; 
        i++; 
        k++; 
    } 
  
    /* Copy the remaining elements of R[], if there 
       are any */
    while (j < n2) 
    { 
        arr[k] = R[j]; 
        j++; 
        k++; 
    } 
} 
  
/* l is for left index and r is right index of the 
   sub-array of arr to be sorted */
void mergeSort(int arr[], int l, int r) 
{ 
    int *count;
    if (l < r) 
    { 
        // Same as (l+r)/2, but avoids overflow for 
        // large l and h 
        int m = l+(r-l)/2; 
  
        // Sort first and second halves 
        mergeSort(arr, l, m); 
        mergeSort(arr, m+1, r); 
  
        merge(arr, l, m, r, count); 
    } 
} 

int fastinversioncount(int arr[], int n){
    int *count;
    *count = 0;
    int *arr2 = new int [n];
    for (int h =0; h < n; h++){
        arr2[h] = arr[h];
    }
    mergeSort(arr2, 0, n);
    return *count;     
}

int main(){
    int U[5] ={3,2,1,4,1};
    std::cout << fastinversioncount(U, 4) << std::endl;
}