栈实现队列

class Queue(object):
    def __init__(self):
        self.stack_a = []
        self.stack_b = []

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

    def pop(self):
        if not self.stack_a:
            while self.stack_a:
                self.stack_b.append(self.stack_a.pop())
        return self.stack_b.pop()

a = [1,2,3,4]
print(a.pop())
print(a)

>>4
>>[1, 2, 3]