input: Write a python function to find the maximum element in a list.
  assert find_max_element([7, 2, 3, 6, 5]) == 7
  assert find_max_element([1, 9, 3, 4, 2]) == 9
  assert find_max_element([-10, -5, -20, -1]) == -1
output: def find_max_element(lst):
      if not lst:
          return None
      max_element = lst[0]
      for num in lst[1:]:
          if num > max_element:
              max_element = num
      return max_element