new_contents: #!/usr/bin/env python
  # -*- coding: utf-8 -*-
  # @Author: Zeyuan Shang
  # @Date:   2016-01-12 18:38:36
  # @Last Modified by:   Zeyuan Shang
  # @Last Modified time: 2016-01-12 18:38:44
  class Solution(object):
      def isPowerOfThree(self, n):
          """
          :type n: int
          :rtype: bool
          """
          return n > 0 and 3 ** round(math.log(n, 3)) == n
subject: add power-of-three