def __init__(self):
self.inp = Stack()
self.out = Stack()
class Queue:
def __init__(self):
self.inp = Stack()
self.out = Stack()
def is_empty(self):
return self.size() == 0
def enqueue(self, item):
self.inp.push(item)
def peek(self):
self.check_out()
return self.out.peek()
def dequeue(self):
self.check_out()
return self.out.pop()
def check_out(self):
if self.out.is_empty():
while not self.inp.is_empty():
self.out.push(self.inp.pop())
def size(self):
return self.inp.size() + self.out.size()