<s>[INST] ### Description

This program implements the merge sort algorithm, a divide-and-conquer technique to sort lists of elements. Here are the steps it follows:

-   If the list is empty or has one element, it is already sorted, so return the list.
-   Find the middle of the list.
-   Split the list into two halves.
-   Recursively call merge\_sort on each half.
-   Merge the two sorted halves into a single sorted list.

### Implementation

```
def merge_sort(arr):
    # Base case: If the length of the array is 1 or less, it is already sorted
    if len(arr) <= 1:
        return arr
    
    # Find the middle of the array
    mid = len(arr) // 2
    
    # Split the array into two halves
    left_half = arr[:mid]
    right_half = arr[mid:]
    
    # Recursively call merge_sort on each half
    left_half = merge_sort(left_half)
    right_half = merge_sort(right_half)
    
    # Merge the two sorted halves into a single sorted list
    return merge(left_half, right_half)


def merge(left, right):
    merged = []
    left_index = 0
    right_index = 0
    
    # Merge smaller elements first
    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
    
    # If there are remaining elements in either the left or right lists, append them to the merged list
    merged.extend(left[left_index:])
    merged.extend(right[right_index:])
    
    return merged

# Test the function with a list of numbers
numbers = [64, 34, 25, 12, 22, 11, 90]
sorted_numbers = merge_sort(numbers)
print("Sorted list:", sorted_numbers)

# Test the function with a list of strings
words = ["dog", "cat", "elephant", "bird", "lion"]
sorted_words = merge_sort(words)
print("Sorted list:", sorted_words)

```

### What I'm struggling with

I'm struggling with the merging part of the merge sort algorithm. I don't understand why we need to merge the two halves of the array after they are sorted.

### What I'm looking for

I'm looking for help understanding the merging part of the merge sort algorithm and how it contributes to the overall sorting process. I'd love an explanation and, if possible, some visual aids to illustrate the merging process.

### Additional context

The implementation of merge sort is in Python, but I'm open to explanations in any programming language. I've tried to follow along with online tutorials, but I still don't fully grasp the merging step.

The main challenge I'm facing is understanding why we need to merge the two halves of the array. Can't we just sort each half individually and call it a day?[/INST]