[LeetCode326] Power of Three

题目：

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?

分类：Math 

代码：

class Solution {
public:
    bool isPowerOfThree(int n) {
        if(n <= 0)
            return false;
        double res = log10(n) / log10(3);
        //floor(x)返回小于x的最大整数 如floor(1.2) = 1
        //ceil(x)返回的是大于x的最小整数 ceil(1.2) = 2
        return res == floor(res);
    }
};