LeetCode #326 - Power of Three

题目描述：

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

Example 1:

Input: 27
Output: true

Example 2:

Input: 0
Output: false

Example 3:

Input: 9
Output: true

Example 4:

Input: 45
Output: false

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

判断一个数是否为3的幂，不能使用循环或者递归，可以利用log函数，如果结果为整数，说明这个数是3的幂。

class Solution {
public:
    bool isPowerOfThree(int n) {
        if(n<=0) return false;
        double x=log10(n)/log10(3);
        if(ceil(x)==floor(x)) return true;
        else return false;
    }
};