input: Write a function to remove duplicates from a given list and return the list in the same order as the input list. If the list is empty, return an empty list.
  assert remove_duplicates([1, 2, 3, 4, 3, 2, 1])==[1, 2, 3, 4]
  assert remove_duplicates([5, 6, 5, 7])==[5, 6, 7]
  assert remove_duplicates([8, 8, 8])==[8]
  assert remove_duplicates([])==[]
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for item in lst:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result