*Ugly number

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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.

题目大意：

编写程序判断一个给定的数字是否为“丑陋数” ugly number

丑陋数是指只包含质因子2, 3, 5的正整数。例如，6, 8是丑陋数而14不是，因为它包含额外的质因子7

注意，数字1也被视为丑陋数

解题思路：

将输入数重复除2, 3, 5，判断得数是否为1即可

时间复杂度：

记num = 2^a * 3^b * 5^c * t，程序执行次数为 a + b + c，换言之，最坏情况为O(log num)

 1 public class Solution {
 2     public boolean isUgly(int num) 
 3     {
 4         if(num <= 0) return false;
 5         int [] prime = {2,3,5};
 6         for (int x:prime)
 7         {
 8             while(num%x==0)
 9             num/=x;
10         }
11         
12         return num==1;
13         
14     }
15 }

reference: http://bookshadow.com/weblog/2015/08/19/leetcode-ugly-number/

*Ugly number

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原文地址：http://www.cnblogs.com/hygeia/p/4777547.html