new_contents: #!/usr/bin/env python
  # encoding: utf-8
  
  """
  implement-stack-using-queues.py
   
  Created by Shuailong on 2016-02-22.
  
  https://leetcode.com/problems/implement-stack-using-queues/.
  
  """
  
  from collections import deque
  
  class Stack(object):
      def __init__(self):
          """
          initialize your data structure here.
          """
          # Using deque to implement queue.
          # push = deque.append()
          # pop = deque.popleft()
          # peek = deque[-1]
          # size = len(deque)
          # isempty = deque
          self.q1 = deque()
          self.q2 = deque()
  
      def __repr__(self):
          s = '['
          for element in self.q1:
              s += str(element) + ' '
          s += ']'
          s += ' ['
          for element in self.q2:
              s += str(element) + ' '
          s += ']'
          return s
  
  
  
      def push(self, x):
          """
          :type x: int
          :rtype: nothing
          """
          self.q1.append(x)
          
  
      def pop(self):
          """
          :rtype: nothing
          """
          while len(self.q1) != 1:
              self.q2.append(self.q1.popleft())
          self.q1.popleft()
          while self.q2:
              self.q1.append(self.q2.popleft())
  
  
      def top(self):
          """
          :rtype: int
          """
          while len(self.q1) != 1:
              self.q2.append(self.q1.popleft())
          res = self.q1.popleft()
          while self.q2:
              self.q1.append(self.q2.popleft())
          self.q1.append(res)
  
          return res
  
      def empty(self):
          """
          :rtype: bool
          """
          return len(self.q1) == 0
          
  
  def main():
      stack = Stack()
      print stack.empty()
      stack.push(1)
      stack.push(2)
      stack.push(3)
      print stack
      print stack.top()
      print stack
      print stack.empty()
      stack.pop()
      print stack
      stack.pop()
      print stack.top()
      stack.pop()
      print stack.empty()
      
  if __name__ == '__main__':
      main()
  
          
subject: solve 1 problem