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?*/
public class PowerOfThree {
    private  static final double EX=10e-15;

    public static void main(String[] args) {
        // TODO Auto-generated method stub
    int d=243;
        System.out.println(isPowerOfThree(d));
    }

     public static boolean isPowerOfThree(int n) {
            if(n==0)
                return false;
            double res=Math.log(n)/Math.log(3);
            System.out.println(res);
            return (Math.abs((res-Math.round(res)))<EX);  //注意为什么不能用floor和ceil   注意double   其实还可以bigdecimal？
        }
    }