[Leetcode]326. Power of Three

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?

class Solution {
public:
    bool isPowerOfThree(int n) {
        double a = log10 (n) /log10 (3);
        return (a - (int) a) == 0? true : false;
    }
};