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 <iostream>

class mergeSort
{
	private:
		int *arr;
		int size;

	public:
		mergeSort(int *arr, int size);
		void sort();
		void print();
		void merge(int l, int m, int r);
};

mergeSort::mergeSort(int *arr, int size)
{
	this->arr = arr;
	this->size = size;
}

void mergeSort::sort()
{
	mergeSort::merge(0, size/2, size-1);
}

void mergeSort::merge(int l, int m, int r)
{
	int i, j, k;
	int n1 = m - l + 1;
	int n2 =  r - m;
	int L[n1], R[n2];

	for (i = 0; i < n1; i++)
		L[i] = arr[l + i];
	for (j = 0;