每日算法题: Queue Using Two Stacks

Hi, here's your problem today. This problem was recently asked by Apple:

Implement a queue class using two stacks. A queue is a data structure that supports the FIFO protocol (First in = first out). Your class should support the enqueue and dequeue methods like a standard queue.

Here's a starting point:

class Queue:

  def __init__(self):

    # Fill this in.

    

  def enqueue(self, val):

    # Fill this in.



  def dequeue(self):

    # Fill this in.



q = Queue()

q.enqueue(1)

q.enqueue(2)

q.enqueue(3)

print q.dequeue()

print q.dequeue()

print q.dequeue()

# 1 2 3