Power of Three

一、题目

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?

二、解决方案

1.使用loop

/**
 * @param {number} n
 * @return {boolean}
 */
var isPowerOfThree = function(n) {
    if(n<1){
        return false;
    }
   while(n%3===0){
       n = n/3;
   }
    return n===1; 
};

除以3一直到1为止，注意代码能简略就简略，还要考虑边界值。

Notice that we need a guard to check that n != 0, otherwise the while loop will never finish 

时间复杂度： O(log_b(n))

空间复杂度：O(1)

2.