input: Write a function to print the unique elements of a given list without using any additional data structures.
  assert print_unique([3, 4, 5, 1, 2])==None
  assert print_unique([3, 5, 10, 1, 2])==None
  assert print_unique([4, 3, 1, 2])==None
  assert print_unique([3, 5, 4, 1, 2])==None
  assert print_unique([])==None
output: def print_unique(lst):
      for i in range(len(lst)):
          if lst[i] not in lst[:i]:
              print(lst[i])