剑指offer python版 9.1用两个栈实现队列

'''
用两个栈来实现一个队列，完成队列的Push和Pop操作。 队列中的元素为int类型。
'''

class Solution:
    def __init__(self):
        self.stack1 = []
        self.stack2 = []

    def push(self, node):
        self.stack1.append(node)

    def pop(self):
        if len(self.stack1) == 0 and len(self.stack2) == 0:
            return
        elif len(self.stack2) == 0:
            while len(self.stack1) > 0:
                self.stack2.append(self.stack1.pop())
        return self.stack2.pop()

if __name__ == '__main__':
    solution = Solution()
    solution.push(1)
    solution.push(2)
    solution.push(3)
    print(solution.pop())
    solution.push(4)
    print(solution.pop())
    print(solution.pop())
    print(solution.pop())