Power of Three ，判断一个数是否为3的n次幂

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?

=========================================常规方法==================================

   public boolean isPowerOfThree(int n) {
        if(n<=0){
            return false;
        }
        // double num=Math.log(n)/Math.log(3); log()与log10()与log1p()的区别
        double num=Math.log10(n)/Math.log10(3);
        if(num%1==0){
            return true;
        }else{
            return false;
        }
    }

=============================流氓方法=================================

public class Solution {
public boolean isPowerOfThree(int n) {
    // 1162261467 is 3^19,  3^20 is bigger than int  
    return ( n>0 &&  1162261467%n==0);
}
}

//1162261467是32位系统中，3的最高次幂19