LeetCode Top Interview Questions 326. Power of Three (Java版; Easy)

绝地灬酷狼 2023-07-02 09:28 10阅读 0赞

### [welcome to my blog][] ###

## LeetCode Top Interview Questions 326. Power of Three (Java版; Easy) ##

#### 题目描述 ####

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?

#### 第一次做; 数学分析:3^19的因数只有20个, 分别是3^0,…3^19 ####

class Solution { 
        public boolean isPowerOfThree(int n) { 
            // 1162261467 is 3^19, 3^20 is bigger than int 
            return (n>0 && 1162261467%n==0)
        }
    }

#### 第一次做;特殊情况:0不是3的幂, 1是3的幂; 三的幂的因数只有三; %3==0的数不一定是3的幂, 比如15, 45; 但3的幂%3==0 ####

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

#### [力扣官方题解][Link 1]; 3^19的因数只有3^0, 3^1, 3^2,…3^19 ####

![format_png][]

#### [力扣官方题解][Link 1]; 比我的递归逻辑清晰 ####

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

[welcome to my blog]: https://littlehaes.com
[Link 1]: https://leetcode-cn.com/problems/power-of-three/solution/3de-mi-by-leetcode/
[format_png]: https://imgconvert.csdnimg.cn/aHR0cHM6Ly9ub3RlLnlvdWRhby5jb20veXdzL3B1YmxpYy9yZXNvdXJjZS8yOGE0OGE3NTE3ODJhOTRiMTQzYjUxNGI2MmQ4MjMzNC94bWxub3RlL0Q1MjMwQUM2QUQ4QjQ0MDZCODFCMTgwQzQ5RjdEMjdGLzU2MTg3?x-oss-process=image/format,png