用两个栈实现队列

# -*- coding:utf-8 -*-
class Queue:
    def __init__(self):
        self.stack_in = []
        self.stack_out = []
    
    
    def push(self, node):
        # write code here
        self.stack_in.append(node)
        
    def pop(self):
        if self.stack_out == []:
            while self.stack_in != []:
                self.stack_out.append(self.stack_in.pop())
        return self.stack_out.pop()
        # return xx


class Stack:
    def __init__(self):
        self.queue_in = []
        self.queue_out = []
    
    
    def push(self, node):
        # write code here
        if len(self.queue_out) > 0:
            self.queue_out.insert(0, node)
        elif len(self.queue_in) >= 0:
            self.queue_in.insert(0, node)

        
    def pop(self):
        if len(self.queue_in) >= 1:
            while len(self.queue_in) > 1:
                 self.queue_out.insert(0, self.queue_in.pop())
            if len(self.queue_in) == 1:
                return self.queue_in.pop()
        else:
            while len(self.queue_out) > 1:
                 self.queue_in.insert(0, self.queue_out.pop())
            if len(self.queue_out) == 1:
                return self.queue_out.pop()
        return None

if __name__ == '__main__':
    q = Queue()
    q.push(1)
    q.push(2)
    q.push(3)
    print q.pop(), q.pop(), q.pop()

    s = Stack()
    s.push(1)
    s.push(2)
    s.push(3)
    s.push(4)
    s.push(5)

    print s.pop(), s.pop(), s.pop(), s.pop(), s.pop()