Merge Sort - Chia để trị

#include <bits/stdc++.h>

using namespace std;

void merge(int arr[], 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; j < n2; j++)
        R[j] = arr[m + 1+ j];

    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2)
    {
        if (L[i] >= R[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = R[j];
            j++;
        }
        k++;
    }

    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }

    while (j < n2)
    {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(int arr[], int l, int r)
{
    if (l < r)
    {
        int m = l+(r-l)/2;

        mergeSort(arr, l, m);
        mergeSort(arr, m+1, r);

        merge(arr, l, m, r);
    }
}

void printArray(int A[], int size)
{
    for (int i = 0; i < size; i++)
        cout << A[i] << " ";
}

int main()
{
    int n;
    cout<<"Nhap so phan tu cua mang: ";
    cin>>n;
    int arr[n];
    cout<<"Nhap gia tri cua cac phan tu cua mang: ";
    for (int i=0;i<n;i++)
    {
        cin>>arr[i];
    }

    cout << "Given array is \n";
    printArray(arr, n);

    mergeSort(arr, 0, n - 1);

    cout << "\nSorted array is \n";
    printArray(arr, n);
    return 0;
}