input: Write a python function to remove duplicate elements from a list while preserving the order.
  assert remove_duplicates([1, 2, 2, 3, 4, 4, 5]) == [1, 2, 3, 4, 5]
  assert remove_duplicates([10, 10, 20, 30, 20, 40, 50, 50]) == [10, 20, 30, 40, 50]
  assert remove_duplicates(['a', 'b', 'a', 'c', 'b']) == ['a', 'b', 'c']
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