原题链接在这里:https://leetcode.com/problems/power-of-three/

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?

题解:

检查能否被3整除,然后整除,看能否一直除到1.

Time Complexity: O(logn).

Space: O(1).

AC Java:

 public class Solution {
public boolean isPowerOfThree(int n) {
if(n<=0){
return false;
}
while(n%3 == 0){
n /= 3;
}
return n==1;
}
}

Follow up 不用 loop. 整数范围内最大的3的幂数, 3^19 = 1162261467能否被n整除.

Time Complexity: O(1). Space: O(1).

AC Java:

 public class Solution {
public boolean isPowerOfThree(int n) {
return n>0 && 1162261467%n==0;
}
}

类似Power of Two.

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