03_3的幂

# 使用了循环 不符合要求
class Solution(object):
    def isPowerOfThree(self, n):
        """
        :type n: int
        :rtype: bool
        """
        while True:
            if n % 3 == 0:
                if n == 3:
                    return True
                n /= 3
            else:
                return False


class Solution2(object):
    def isPowerOfThree(self, n):
        """
        :type n: int
        :rtype: bool
        """
        return n > 0 and 3 ** 19 % n == 0


class Solution3(object):
    def isPowerOfThree(self, n):
        """
        :type n: int
        :rtype: bool
        """
        if n < 1:
            return False
        while n % 3 == 0:
            n /= 3
        return n == 1




n = 27
s = Solution()
print(s.isPowerOfThree(n))