Write a C ++ program to implement Merge Sort algorithm to efficiently handle an input array that may contain duplicate elements. The goal is to modify the algorithm in such a way that duplicate elements appear in the sorted array in the same order as they appear in the input.

#include <stdio.h>
#include <iostream>
using namespace std;

void merge(int *array, int l, int m, int r)
{
    int i, j, k, nl, nr;
    //size of left and right sub-arrays
    nl = m-l+1; nr = r-m;
    int larr[nl], rarr[nr];
    //fill left and right sub-arrays
    for(i = 0; i<nl; i++)
        larr[i] = array[l+i];
    for(j = 0; j<nr; j++)
        rarr[j] = array[m+1+j];
    i = 0; j = 0; k = l;
    //marge temp arrays to real array
    while(i < nl && j<nr)
    {
        if(larr[i] <= rarr[j])
        {
            array[k] = larr[i];
            i++;
        }
        else