class Queue:
def __init__(self):
self._data_stack = Stack()
self._utility_stack = Stack()
# Complexity: 2 * O(n)?? for 2 for loops, but not nested!
def enqueue(self, item):
if self._data_stack.__len__() < 1:
self._data_stack.push(item)
return
for _ in range(
self._data_stack.__len__()
): # "_" instead of an i variable means you don't care about the variable (saves memory)
popped_item = self._data_stack.pop()
self._utility_stack.push(popped_item)
self._data_stack.push(item)
for _ in range(self._utility_stack.__len__()):
self._data_stack.push(self._utility_stack.pop())
#everything is on the data stack in the original order
# Complexity: O(1)
def dequeue(self):
if self._data_stack.__len__() < 1:
raise Exception("queue is empty")
return self._data_stack.pop()
# pop removes the data item that's been there the longest, when in a queue
def __len__(self):
return len(self._data_stack)
def test_push_len(self):
#Arrange
my_stack = Stack()
my_stack.push(1)
my_stack.push(2)
my_stack.push(3)
#Act
length = my_stack.__len__()
#Assert
self.assertEqual(3, length, "len did not return correct length")
