new_contents: class Solution:
      # @param {integer} n
      # @return {boolean}
  
      def isPowerOfTwo(self, n):
          cnt = 0
          while n:
              if n & 1:
                  cnt += 1
              if cnt > 1:
                  return False
              n >>= 1
          return cnt == 1
  
subject: add solution for Power of Two