Python Merge Sort Algorithm Implementation

Code Analysis and Issue:

The provided Python code implements the merge sort algorithm. However, a key issue arises in this implementation due to the absence of the merge function definition within the given code snippet.

Review of Previous Attempts:

The existing code attempts to recursively divide the array in merge_sort function and merge the sorted halves. However, the missing implementation of the merge function leads to a NameError when running the script.

Proposed Solution:

To resolve the issue, the merge function needs to be defined in the code. Here is the missing merge function included in the provided script:

def merge(left, right):
    result = []
    i = j = 0
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1
    result.extend(left[i:])
    result.extend(right[j:])
    return result

By adding the merge function definition, the code will perform the merge step correctly and execute the merge sort algorithm flawlessly. The corrected script will now produce the sorted array as intended.

Code Development:

def merge_sort(arr):
    if len(arr) <= 1:
        return arr
    middle = len(arr) // 2
    left = merge_sort(arr[:middle])
    right = merge_sort(arr[middle:])
    return merge(left, right)

def merge(left, right):
    result = []
    i = j = 0
    while i < len(left) and j < len(right):
        if left[i] < right[j]:
            result.append(left[i])
            i += 1
        else:
            result.append(right[j])
            j += 1
    result.extend(left[i:])
    result.extend(right[j:])
    return result

arr = [54, 26, 93, 17, 77, 31, 44, 55, 20]
print(merge_sort(arr))

Code Usage Example:

This corrected code snippet showcases the merge sort algorithm implementation in Python. It can be utilized to efficiently sort lists or arrays in ascending order.

By executing the provided script, the output will display the sorted array generated by the merge sort algorithm.