input: Write a python function to find duplicate elements in a list.
  assert find_duplicates([1, 2, 3, 4, 5, 6, 2, 4, 7, 8]) == [2, 4]
  assert find_duplicates([10, 20, 30, 40, 50, 10, 30, 60]) == [10, 30]
  assert find_duplicates([100, 200, 300, 100, 400, 500, 200, 600]) == [100, 200]
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)