Mergesort recursive algorithm

Mergesort.java

public class MergeSort {
	
	public static void main (String args[]) {
		int[] arr = new int[]{5, 2, 3, 1, 4};
        int[] helperArr = new int[arr.length];
		mergeSort(arr, helperArr, 0, arr.length-1);

        for (int i : arr) {
            System.out.print(i + " ");
        }
	}
	
	public static void mergeSort(int[] arr, int[] helperArr, int start, int end) {

		// base case
		if (start >= end) return;
		
		int mid = (start + end) / 2;
		// sort first half
		mergeSort(arr, helperArr, start, mid);
		// sort second half
		mergeSort(arr, helperArr, mid + 1, end);
		// combine both halves together
		merge(arr, helperArr, start, mid, mid + 1, end);
	}
	
	public static void merge(int[] arr, int[] helperArr, int firstStart, int firstEnd, int lastStart, int lastEnd) {

		int firstPtr = firstStart;
		int lastPtr = lastStart;
		int index = firstPtr;

        for (int i = firstPtr; i <= lastEnd; i++) {
        helperArr[i] = arr[i];
        }
	
		while (firstPtr <= firstEnd || lastPtr <= lastEnd) {
			if (firstPtr <= firstEnd && lastPtr <= lastEnd) {
					if (helperArr[firstPtr] <= helperArr[lastPtr]) {
						arr[index] = helperArr[firstPtr];
						index++;
						firstPtr++;
					} else {
						arr[index] = helperArr[lastPtr];
						index++;
						lastPtr++;
					}
			} else if (firstPtr <= firstEnd) {
				arr[index] = helperArr[firstPtr];
				index++;
				firstPtr++;
			} else {
				arr[index] = helperArr[lastPtr];
				index++;
				lastPtr++;
			}
		}	
	}
}
//reference: https://www.geeksforgeeks.org/merge-sort/