Jan 14 - Power of three; Math; Integer; Digit;

No loop; No recursion; 我没找到规律 但是从讨论区看到别人的思路：

If N is a power of 3:

• It follows that 3^X == N
• It follows that log (3^X) == log N
• It follows that X log 3 == log N
• It follows that X == (log N) / (log 3)
• For the basis to hold, X must be an integer.

代码：

public class Solution {
    public boolean isPowerOfThree(int n) {
        double diff = 10e-15;
        double x = Math.log(n)/Math.log(3);
        return Math.abs( x - Math.round(x)) <= diff;
    }
}