Python code for merge sort algorithm for sorting n numbers. The running time of this algorithm is: O(n . lg(n) )

MergeSort.py

def merge(arr, start, middle, end):
    i = j = 0
    k = start
    left = arr[start:middle]
    right = arr[middle:end]
    
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            arr[k] = left[i]
            i += 1
        else:
            arr[k] = right[j]
            j+= 1
        k += 1
        
    while i < len(left):
        arr[k] = left[i]
        i += 1
        k += 1
        
    while j < len(right):
        arr[k] = right[j]
        j += 1
        k += 1


def mergeSort(arr, end, start = 0):
    if end == start +1:
        return arr[start]
    
    middle = (start + end) // 2
    mergeSort(arr, middle, start)
    mergeSort(arr, end, middle)
    merge(arr, start, middle, end)


size = int(input('Enter the size of the array: '))
arr = []
for i in range(size):
    element = int(input(f'Enter the number {i + 1}: '))
    arr.append(element)
print("The unsorted array is : " + str(arr))
mergeSort(arr, size)
print("The sorted array is : " + str(arr))