input: Write a function named `remove_duplicates` that takes a list of integers as input and returns a new list with all duplicate elements removed while preserving the original order. If the input list is empty, the function should return an empty list.
  
  assert remove_duplicates([1, 3, 3, 5, 5, 7]) == [1, 3, 5, 7]
  assert remove_duplicates([2, 4, 2, 4, 6]) == [2, 4, 6]
  assert remove_duplicates([7, 7, 7]) == [7]
  assert remove_duplicates([1, 2, 3, 4]) == [1, 2, 3, 4]
  assert remove_duplicates([]) == []
output: def remove_duplicates(lst):
      seen = set()
      result = []
      for num in lst:
          if num not in seen:
              seen.add(num)
              result.append(num)
      return result