LeetCode: Ugly Number

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题目链接：https://leetcode.com/problems/ugly-number/

题目：

Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number.

题目理解：判断一个给定的数是否是丑数。所谓丑数，就是那些因子只含2,3,5的数。1是自小丑数

最直接的代码如下：

public class Solution {
    public boolean isUgly(int num) {
        if(num <= 0) 
            return false;
        if(num == 1) {
            return true;
         }
        while(num % 2 == 0) {
  	  num /= 2;
         }
  
        while(num % 3 == 0) {
  	  num /= 3;
         }
  
        while(num % 5 == 0) {
 	   num /= 5;
         }
  
        return num == 1 ? true : false;	
    }
}

结果超时。。。

然后改进了一下，AC。代码如下：

public class Solution {
    public boolean isUgly(int num) {
        if(num <= 0) 
            return false;
        if(num == 1) {
            return true;
        }
    	if(num % 5 == 0) {
    	    return isUgly(num / 5);
    	} else if(num % 3 == 0) {
    	    return isUgly(num / 3);
    	} else if(num % 2 == 0) {
    	    return isUgly(num / 2);
    	} else {
    	    return false;
    	}
		
    }
}

LeetCode: Ugly Number

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原文地址：http://blog.csdn.net/yangyao_iphone/article/details/47777335