326. 3的幂

以你之姓@ 2023-02-11 07:12 19阅读 0赞

# 题目来源 #

[LEETCODE][]

# 题目描述 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]

# 题目解析 #

## 递归 ##

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

![在这里插入图片描述][20200522094644110.png]

## 常规解法 ##

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

public boolean isPowerOfThree(int n) {
        
    		if (n == 1) return true;
    		if (n < 3) return false;  //负数不可能
    		while (n > 3)
    		{
        
    			if (n % 3 != 0) return false;
    			n = n / 3;
    		}
    		return n == 3;
        }

public boolean isPowerOfThree(int n) {
        
    		while (n && n %3 == 0)   //注意一定要添加n&& ,因为如果n=0，那么n %3 一定为0， 会陷入死循环
    		{
        
    			n = n / 3;
    		}
    		return n == 1;
        }

3的幂次的质因子只有3，而所给出的n如果也是3的幂次，故而题目中所给整数范围内最大的3的幂次的因子只能是3的幂次，1162261467是3的19次幂，是整数范围内最大的3的幂次

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

![在这里插入图片描述][2020052209174275.png]

## 硬编码 ##

public static boolean isPowerOfThree(int n) {
        
            if (n == 1 || n == 3 || n == 9 || n == 27 || n == 81 || n == 243 || n == 729 || n == 2187 || n == 6561 || n == 19683 || n == 59049 || n == 177147 || n == 531441 || n == 1594323 || n == 4782969 || n == 14348907 || n == 43046721 || n == 129140163 || n == 387420489 || n == 1162261467) {
        
                return true;
            } else {
        
                return false;
            }
        }

## 基准转换 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70 1]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70 2]

public class Solution {
        
        public boolean isPowerOfThree(int n) {
        
            return Integer.toString(n, 3).matches("^10*$");
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70 3]

java中浮点数比较就是个坑

[LEETCODE]: https://leetcode-cn.com/problems/power-of-three/
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/2020052209434540.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3poaXpoZW5nZ3Vhbg==,size_16,color_FFFFFF,t_70
[20200522094644110.png]: https://img-blog.csdnimg.cn/20200522094644110.png
[2020052209174275.png]: https://img-blog.csdnimg.cn/2020052209174275.png
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