Given an integer, write a function to determine if it is a power of three.

Follow up:
​ Could you do it without using any loop / recursion?

思路

如果单纯利用循环，其实还是很好做的。

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

但是不利用循环的方法实在是想不出来……就看看这篇参考资料吧：

https://discuss.leetcode.com/topic/33536/a-summary-of-all-solutions-new-method-included-at-15-30pm-jan-8th