input: Write a function to find duplicates in a list.
  assert find_duplicates([1, 2, 3, 2, 4, 5, 6, 1, 7, 8, 8]) == [2, 1, 8]
  assert find_duplicates([10, 20, 30, 40, 50, 60]) == []
  assert find_duplicates(['a', 'b', 'c', 'a', 'd', 'b', 'e']) == ['a', 'b']
output: def find_duplicates(lst):
      seen = set()
      duplicates = set()
      for item in lst:
          if item in seen:
              duplicates.add(item)
          else:
              seen.add(item)
      return list(duplicates)