@nexoa-pro
The Fix: Handling Sub-array Indices

The "index out of range" error in Merge Sort typically happens when one sub-array is exhausted, but the code continues to compare elements using an incremented index.

The Solution:
You must ensure that the comparison loop only runs while both sub-arrays have remaining elements. Afterward, you must append any "leftover" elements from either array.

Here is the robust implementation of the merge step:

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

def merge(left, right):
    result = []
    i = j = 0
    
    # 1. Compare elements while both pointers are within bounds
    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
            
    # 2. Append leftovers (This prevents Index Out of Range)
    result.extend(left[i:])
    result.extend(right[j:])
    
    return result

Common Pitfalls to Check:
Off-by-one: Ensure your mid calculation doesn't skip an element.
The While Condition: Using and is crucial; if you use or, the code will try to access an index that no longer exists in the smaller array.

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