input: Write a python function to find the maximum difference between any two elements in a list.
  assert max_difference([1, 2, 3, 8, 9]) == 8
  assert max_difference([10, 15, 3, 7, 19]) == 16
  assert max_difference([1, 1, 1, 1]) == 0
output: def max_difference(lst):
      if not lst or len(lst) < 2:
          return 0
      return max(lst) - min(lst)