Merge sort

#include <iostream>

using namespace std;

void merge(int arr[], int l, int m, int r) {
  int n1 = m - l + 1;
  int n2 = r - m;

  int L[n1], R[n2];

  for (int i = 0; i < n1; i++)
    L[i] = arr[l + i];
  for (int j = 0; j < n2; j++)
    R[j] = arr[m + 1 + j];

  int i, j, k;
  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)
    return;

  int m = l + (r - l) / 2;

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

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

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

int main() {
  int arr[] = {6, 5, 12, 10, 9, 1};
  int size = sizeof(arr) / sizeof(arr[0]);

  mergeSort(arr, 0, size - 1);

  cout << "Sorted array: \n";
  printArray(arr, size);
  return 0;
}