#! /usr/bin/env python

# -*- coding: utf-8 -*-

# @Author: xuezaigds@gmail.com

class Queue(object):

"""

Use python list as the underlying data structure for stack.

Add a "move()" method to simplify code: it moves all elements

of the "inStack" to the "outStack" when the "outStack" is empty.

"""

def __init__(self):

self.in_stack, self.out_stack = [], []

def push(self, x):

self.in_stack.append(x)

def pop(self):

self.move()

self.out_stack.pop()

def peek(self):

self.move()

return self.out_stack[-1]

def empty(self):

return (not self.in_stack) and (not self.out_stack)

def move(self):

if not self.out_stack:

while self.in_stack:

self.out_stack.append(self.in_stack.pop())

'''

if __name__ == '__main__':

q = Queue()

q.push(2)

q.push(3)

q.push(4)

print q.peek()

q.pop()

print q.peek()

q.pop()

q.pop()

print q.empty()

'''