class PseudoQueue:
"""Queue data structure made with Stack data structure under the hood."""
def __init__(self):
"""PseudoQueue constructor."""
self.stack_one = Stack()
self.stack_two = Stack()
self.size = 0
def enqueue(self, value):
"""Add a value to the rear of the pseudo queue."""
for _ in range(self.size):
node_value = self.stack_one.pop()
self.stack_two.push(node_value)
self.stack_two.push(value)
self.size += 1
for _ in range(self.size):
node_value = self.stack_two.pop()
self.stack_one.push(node_value)
def dequeue(self):
"""Remove a value from the front of the pseudo queue."""
if not self.size:
return EmptyQueueException()
return self.stack_one.pop()
def peek(self):
"""See the pseudo front queue value."""
return self.stack_one.peek()
def test_push_onto_full():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
actual = s.top.value
expected = "cucumber"
assert actual == expected
def test_peek():
s = Stack()
s.push("apple")
s.push("banana")
actual = s.peek()
expected = "banana"
assert actual == expected
def test_check_not_empty():
s = Stack()
s.push("apple")
s.push("banana")
actual = s.is_empty()
expected = False
assert actual == expected
def __init__(self):
"""AnimalShelter constructor."""
self.main_stack = Stack()
self.helper_stack = Stack()
class AnimalShelter:
"""Queue of animals in a shelter."""
def __init__(self):
"""AnimalShelter constructor."""
self.main_stack = Stack()
self.helper_stack = Stack()
def enqueue(self, animal):
"""
Bring an animal into the shelter.
Parameters:
animal (object): The Cat or Dog instance to bring into the shelter.
"""
while not isinstance(self.main_stack.peek(), EmptyStackException):
self.helper_stack.push(self.main_stack.pop())
self.helper_stack.push(animal)
while not isinstance(self.helper_stack.peek(), EmptyStackException):
self.main_stack.push(self.helper_stack.pop())
def dequeue(self, animal):
"""
Take an animal out of the shelter.
Parameters:
animal (class): The Cat or Dog instance which should be taken out of the shelter.
Returns:
(Animal): The instance of the Cat or Dog class first in the queue in the shelter.
"""
if isinstance(self.main_stack.peek(), EmptyStackException):
return EmptyStackException()
saved_animal = None
while not isinstance(self.main_stack.peek(), EmptyStackException):
if not saved_animal and isinstance(self.main_stack.peek(), animal):
saved_animal = self.main_stack.pop()
else:
self.helper_stack.push(self.main_stack.pop())
while not isinstance(self.helper_stack.peek(), EmptyStackException):
self.main_stack.push(self.helper_stack.pop())
return saved_animal
def peek(self):
"""See the first animal in the shelter."""
return self.main_stack.peek()
def test_pop_empty():
s = Stack()
with pytest.raises(InvalidOperationError) as e:
s.pop()
assert str(e.value) == "Method not allowed on empty collection"
def test_pop_until_empty():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
s.pop()
s.pop()
s.pop()
actual = s.is_empty()
expected = True
assert actual == expected
def test_push_onto_empty():
s = Stack()
s.push("apple")
actual = s.top.value
expected = "apple"
assert actual == expected
def test_pop_some():
s = Stack()
s.push("apple")
s.push("banana")
s.push("cucumber")
s.pop()
actual = s.pop()
expected = "banana"
assert actual == expected
def test_pop_single():
s = Stack()
s.push("apple")
actual = s.pop()
expected = "apple"
assert actual == expected
def __init__(self):
"""PseudoQueue constructor."""
self.stack_one = Stack()
self.stack_two = Stack()
self.size = 0