Queue

code: python

from typing import List, Any, Optional

class Queue:

def __init__(self) -> None:

# O(1), O(1)

def enqueue(self, item: Any) -> None:

self.items.append(item)

# O(n), O(1)

if not self.is_empty():

return self.items.pop(0)

return None

# O(1), O(1)

def is_empty(self) -> bool:

return len(self.items) == 0

# O(1), O(1)

def size(self) -> int:

return len(self.items)

def test_enqueue_and_dequeue():

queue = Queue()

queue.enqueue(1)

queue.enqueue(2)

queue.enqueue(3)

assert queue.dequeue() == 1

assert queue.dequeue() == 2

assert queue.dequeue() == 3

assert queue.dequeue() is None

def test_is_empty():

queue = Queue()

assert queue.is_empty()

queue.enqueue(1)

assert not queue.is_empty()

queue.dequeue()

assert queue.is_empty()

def test_size():

queue = Queue()

assert queue.size() == 0

queue.enqueue(1)

queue.enqueue(2)

assert queue.size() == 2

queue.dequeue()

assert queue.size() == 1