system
You are a chatbot acting as a human, specialising in Coding. Give a response that a human will want to hear.
human
Can you explain what these functions do:
```
def merge_sort(arr):
    if len(arr) <= 1:
        return arr

    mid = len(arr) // 2
    left_half = arr[:mid]
    right_half = arr[mid:]

    left_half = merge_sort(left_half)
    right_half = merge_sort(right_half)

    return merge(left_half, right_half)


def merge(left, right):
    merged = []
    left_index = 0
    right_index = 0

    while left_index < len(left) and right_index < len(right):
        if left[left_index] <= right[right_index]:
            merged.append(left[left_index])
            left_index += 1
        else:
            merged.append(right[right_index])
            right_index += 1

    while left_index < len(left):
        merged.append(left[left_index])
        left_index += 1

    while right_index < len(right):
        merged.append(right[right_index])
        right_index += 1

    return merged
```
gpt
The code snippet implements the Merge Sort algorithm which is a sorting algorithm that uses a divide-and-conquer approach. The algorithm recursively divides the input array into two subarrays, sorts them separately and then merges them back in a sorted order. We can go through each function to understand what it is doing.

1. `merge_sort(arr)`: This function takes an array and returns the sorted array.
  - The function has a base case for when the length of the input array is less than or equal to 1 since an array size of 1 means that it is already sorted.
  - If the base case fails, then we continue the algorithm.
  - The algorithm finds the middle of the array and divides the elements into two halves `left_half` and `right_half`.
  - It calls `merge_sort` on these two halves and then returns the merge of the two sorted halves.

2. `merge(left, right)`: This function merges two sorted arrays left and right into one sorted array.
  - It initializes an empty array to store the new array and two variables to store the current index of each array.
  - The algorithm does a while loop until one array is exhausted of elements.
  - Within the loop, the lower of the elements between the current left element and the current right element is stored in the array.
  - After one of the arrays is fully traversed, the remainder of the other array is added to the array.