Merge Sort

Medium

Given an array arr[], its starting position l and its ending position r. Sort the array using merge sort algorithm.
Example 1:

Input:
N = 5
arr[] = {4 1 3 9 7}
Output:
1 3 4 7 9

Example 2:

Input:
N = 10
arr[] = {10 9 8 7 6 5 4 3 2 1}
Output:
1 2 3 4 5 6 7 8 9 10

Your Task:
You don't need to take the input or print anything. Your task is to complete the function merge() which takes arr[], l, m, r as its input parameters and modifies arr[] in-place such that it is sorted from position l to position r, and function mergeSort() which uses merge() to sort the array in ascending order using merge sort algorithm.

Expected Time Complexity: O(nlogn) 

Expected Auxiliary Space: O(n)

Constraints:
1 <= N <= 10⁵
1 <= arr[i] <= 10³