input: Write a function to remove all duplicate elements from a given list of integers. The function should return the list with unique elements in the same order as they first appeared.
  assert remove_duplicates([1, 2, 3, 2, 4, 5, 6, 3])==[1, 2, 3, 4, 5, 6]
  assert remove_duplicates([5, 5, 5, 5, 5])==[5]
  assert remove_duplicates([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert remove_duplicates([])==[]
  assert remove_duplicates([1])==[1]
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