python--两个队列实现一个栈

 

class TwoQueueOneStack(object):
    def __init__(self):
        self.queue1 = []
        self.queue2 = []
    def push(self,item):
        #正常进队列1
        self.queue1.append(item)
    def pop(self):
        #弹出时，把队列1中元素取出到只剩一个为止，放到队里2中
        #队列1和2交换为止
        #弹出队列2中的元素
        if len(self.queue1)==0:
            return None
        while len(self.queue1) !=1:
            self.queue2.append(self.queue1.pop(0))
        self.queue1,self.queue2 = self.queue2,self.queue1
        return self.queue2.pop(0)



stack = TwoQueueOneStack()
stack.push(1)
stack.push(2)
stack.push(3)
stack.push(4)
stack.push(5)
print(stack.pop())
print(stack.pop())
print(stack.pop())
print(stack.pop())
stack.push(6)
print(stack.pop())
print(stack.pop())