old_contents: '''
  In this module, we implement merge sort
  Time complexity: O(n * log n)
  '''
  
  
  def mergesort(arr):
      '''
      Sort array using  mergesort
      
      '''
      pass
      
  
  def _merge(arr):
      pass
  
new_contents: '''
  In this module, we implement merge sort
  Time complexity: O(n * log n)
  '''
  
  
  def mergesort(arr, left, right):
      '''
      Sort array using  mergesort
      
      '''
      if left < right:
          middle = left + (right - left) /2
          mergesort(arr, left, middle)
          mergesort(arr, middle+1, right)
          return merge(arr, left, right)
      
  
  def merge(arr, left, right):
      pass
  
subject: Update mergesort.py