用两个队列实现栈.py

# -*- coding:UTF-8 -*-
'''
两个队列实现栈
'''
class Solution:
    def __init__(self):
        self.queue1 = []
        self.queue2 = []
    def push(self, x):
        if self.queue2 == []:
            self.queue1.append(x)
        else:
            self.queue2.append(x)
    def pop(self):
        if not self.queue1 and not self.queue2:
            return
        if self.queue1 != []:
            length = len(self.queue1)
            for i in range(length-1):
                self.queue2.append(self.queue1.pop(0))
            return self.queue1.pop()
        else:
            length = len(self.queue2)
            for i in range(length-1):
                self.queue1.append(self.queue2.pop(0))
            return self.queue2.pop()

P = Solution()
P.push(10)
P.push(11)
P.push(12)
print(P.pop())
P.push(13)
print(P.pop())
print(P.pop())
print(P.pop())
print(P.pop())