编程题练习 两个栈实现队列

两个栈实现队列

1.判断队列为空： 当栈s1 和 s2都为空时，那么队列为空

2.入队操作: 直接将数据加入到s1栈中

3.出队操作：当 s2 栈不为空的时候， s2 栈直接执行出栈操作就可以得到出队的数据；

　　　　　　如果 s2 栈为空的话，则 s2 入栈 s1 出栈的数据，直到 s2 栈为空。

4.查看队列首数据：和出队操作一样

#!/usr/bin/env python3
# -*- coding: utf-8 -*-


class Queue(object):
        def __init__(self):
                self.s1 = Stack()
                self.s2 = Stack()

        def is_empty(self):
                result =  self.s1.is_empty() and self.s2.is_empty()
                return result

        def enqueue(self, elem):
                self.s1.push(elem)

        def dequeue(self):
                while self.s2.is_empty():
                        while not self.s1.is_empty():
                                self.s2.push(self.s1.pop())
                return self.s2.pop()

        def peek(self):
                while self.s2.is_empty():
                        while not self.s1.is_empty():
                                self.s2.push(self.s1.pop())
                return self.s2.peek()

class Stack(object):
        def __init__(self):
                self._elems = []

        def is_empty(self):
                return self._elems == []

        def push(self, elem):
                self._elems.append(elem)

        def pop(self):
                return self._elems.pop()

        def peek(self):
                return self._elems[-1]

        def bianli(self):
                return self._elems

if __name__ == "__main__":
        s = Stack()
        for i in range(5):
                s.push(i)
        print(s.pop())
        print(s.pop())
        print(s.bianli())
        q = Queue()
        for i in range(5):
                q.enqueue(i)
        print("enqueue 0 1 2 3 4 ")
        print("dequeue:",q.dequeue())
        print("dequeu:",q.dequeue())