input: Write a python function to find duplicate elements in a list.
  assert duplicate_elements([1, 2, 3, 2, 4, 5, 1, 0]) == {1, 2}
  assert duplicate_elements([10, 20, 30, 20, 40, 50, 10, 0]) == {10, 20}
  assert duplicate_elements([5, 6, 7, 8, 5, 9, 10]) == {5}
output: def duplicate_elements(lst):
      seen = set()
      duplicates = set()
      for element in lst:
          if element in seen:
              duplicates.add(element)
          else:
              seen.add(element)
      return duplicates