input: Write a python function to find duplicates in a list.
  assert find_duplicates([1, 2, 3, 4, 5, 6, 2, 3, 7, 8]) == [2, 3]
  assert find_duplicates([10, 20, 30, 40, 50, 60, 70]) == []
  assert find_duplicates([5, 7, 9, 7, 9, 5, 5, 3]) == [7, 9, 5]
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)