input: Write a function to remove all duplicate elements from a list while preserving the original order of the elements. Return the new list without duplicates. If the input list is empty, return an empty list.
  assert remove_duplicates([1, 3, 3, 5, 5, 7])==[1, 3, 5, 7]
  assert remove_duplicates([1, 1, 1, 1, 1])==[1]
  assert remove_duplicates([2, 4, 6, 4, 2])==[2, 4, 6]
  assert remove_duplicates([3, 7, 7, 3])==[3, 7]
  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