code: def next(self):
      """
      :rtype: int
      """
      v = self.queue.pop(0)
      ret = v.pop(0)
      if v:
          self.queue.append(v)
      return ret
  
label_desc: Use image node_id 2 for calling the ZigZagIterator obj's underlying member method code with example usage: obj.next() and returns: ret