Sorting Algorithms – #3 merge Sort

import java.util.Arrays;
public class Main {
    public static void main(String[] args) {

      int[] arr = new int[]{5,9,2,7,1,10,4,1,50};

      System.out.println("unsorted Array : "+Arrays.toString(arr));

      margeSort(arr,0,arr.length-1); 

      System.out.println("sorted Array in ascending order : "+Arrays.toString(arr));
    }

   private static void margeSort(int[] arr,int left,int right){

    // return if arr size becomes 1
    if(left >= right) return;


    // calculate the mid
    int mid = ( left + right ) / 2;

    // divide the array into two subarrays
    margeSort(arr,left,mid);
    margeSort(arr,mid+1,right);

    // merge subarrays
    merge(arr,left,mid,right);

   }

   private static void merge(int[] arr,int left,int mid,int right){

    // calculate the size of left & right subarrays
    int leftArrSize = mid - left+1;
    int rightArrSize = right - mid;

    // initialise temp subarrays
    int[] leftArr = new int[leftArrSize];
    int[] rightArr = new int[rightArrSize];

    // copy left & right array into temp arrays
    for (int i = 0; i < leftArrSize; ++i)
      leftArr[i] = arr[left + i];
    for (int j = 0; j < rightArrSize; ++j)
    rightArr[j] = arr[mid + 1 + j];

    // set initial indexes of subarrays
    int leftPointer = 0;
    int rightPointer = 0;
    int arrPointer = left;

    // copy temp subarrays, in ascending order
    while(leftPointer < leftArrSize && rightPointer < rightArrSize ){

      if(leftArr[leftPointer] <= rightArr[rightPointer]){
        arr[arrPointer] = leftArr[leftPointer];
        arrPointer++;
        leftPointer++;
      }else{
        arr[arrPointer] = rightArr[rightPointer];
        arrPointer++;
        rightPointer++;
      }
    }


    // copy the remaining elements of left subarray into a marge array
    while(leftPointer < leftArrSize){
      arr[arrPointer] = leftArr[leftPointer];
      arrPointer++;
      leftPointer++;
    }

    // copy the remaining elements of right subarray into a merge array
    while(rightPointer < rightArrSize){
      arr[arrPointer] = rightArr[rightPointer];
      arrPointer++;
      rightPointer++;
    }



   }
}