leetcode之Implement Stack using Queues

跟上一篇的Implement Queue using Stacks差不多。唯一一个不同的就是一个是在list后面加一个元素，这个是在头部插一个元素。代码如下：

class Stack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.items = []

def push(self, x):
"""
:type x: int
:rtype: nothing
"""
self.items.insert(0, x)

def pop(self):
"""
:rtype: nothing
"""
del self.items[0]

def top(self):
"""
:rtype: int
"""
return self.items[0]

def empty(self):
"""
:rtype: bool
"""
return len(self.items) == 0