# Learn Data Structures by Building the Merge Sort Algorithm - Step 15

### Tell us what’s happening:

Describe your issue in detail here.

``````def merge_sort(array):

middle_point = len(array) // 2
left_part = array[:middle_point]
right_part = array[middle_point:]

merge_sort(left_part)
merge_sort(right_part)

left_array_index = 0
right_array_index = 0
sorted_index = 0

while left_array_index < len(left_part) and right_array_index < len(right_part):

# User Editable Region

if left_part[left_array_index] < right_part[right_array_index]:
array[sorted_index] = left_part[left_array_index]
left_array_index += 1
else :
array[sorted_index] = right_part[right_array_index]

# User Editable Region

``````

User Agent is: `Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36`

### Challenge Information:

Learn Data Structures by Building the Merge Sort Algorithm - Step 15

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Here the problem was with