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

 1 /**
 2  * @param {number} n
 3  * @return {boolean}
 4  */
 5 var isPowerOfThree = function(n) {
 6     if(n<1){
 7         return false;
 8     }
 9    while(n%3===0){
10        n = n/3;
11    }
12     return n===1; 
13 };

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)