input: Write a python function to perform merge sort on a list.
  assert merge_sort([34, 7, 23, 32, 5, 62]) == [5, 7, 23, 32, 34, 62]
  assert merge_sort([12, 11, 13, 5, 6, 7]) == [5, 6, 7, 11, 12, 13]
  assert merge_sort([4, 3, 2, 10, 12, 1, 5, 6]) == [1, 2, 3, 4, 5, 6, 10, 12]
output: def merge_sort(arr):
      if len(arr) > 1:
          mid = len(arr) // 2
          left_half = arr[:mid]
          right_half = arr[mid:]
  
          merge_sort(left_half)
          merge_sort(right_half)
  
          i = j = k = 0
          
          while i < len(left_half) and j < len(right_half):
              if left_half[i] < right_half[j]:
                  arr[k] = left_half[i]
                  i += 1
              else:
                  arr[k] = right_half[j]
                  j += 1
              k += 1
  
          while i < len(left_half):
              arr[k] = left_half[i]
              i += 1
              k += 1
  
          while j < len(right_half):
              arr[k] = right_half[j]
              j += 1
              k += 1
  
      return arr