/*

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？

        }

    }