from typing import Any, Optional

from adts import Stack, Queue

def peek(stack: Stack) -> Optional[Any]:

"""Return the top item on the given stack.

If the stack is empty, return None.

Unlike Stack.pop, this function should leave the stack unchanged when the

function ends. You can (and should) still call pop and push, just make

sure that if you take any items off the stack, you put them back on!

>>> stack = Stack()

>>> stack.push(1)

>>> stack.push(2)

>>> peek(stack)

2

>>> stack.pop()

2

"""

Enter code here

pass

def reverse_top_two(stack: Stack) -> None:

"""Reverse the top two elements on .

Precondition: has at least two items.

>>> stack = Stack()

>>> stack.push(1)

>>> stack.push(2)

>>> reverse_top_two(stack)

>>> stack.pop()

1

>>> stack.pop()

2

>>> stack.is_empty()

True

"""

Enter code here

pass

def remove_all(queue: Queue) -> None:

"""Remove all items from the given queue.

>>> queue = Queue()

>>> queue.enqueue(1)

>>> queue.enqueue(2)

>>> queue.enqueue(3)

>>> remove_all(queue)

>>> queue.is_empty()

True

"""

Enter code here

pass

def remove_all_but_one(queue: Queue) -> None:

"""Remove all items from the given queue except the last one.

Precondition: contains at least one item.

or: not queue.is_empty()

>>> queue = Queue()

>>> queue.enqueue(1)

>>> queue.enqueue(2)

>>> queue.enqueue(3)

>>> remove_all_but_one(queue)

>>> queue.is_empty()

False

>>> queue.dequeue()

3

>>> queue.is_empty()

True

"""

Enter code here

pass

if __name__ == '__main__':

# import doctest

# doctest.testmod()

# Remember, to get this to work you need to Run this file, not just the

# doctests in this file!

import python_ta

python_ta.check_all(config={

'extra-imports': ['adts']

})