Ugly Number问题及解法

问题描述：

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.

问题分析：

只要一个正整数中的素因子不止2,3,5其中的几个，那么就不是ugly number，所以，我们只需要把该整数所有的2,3,5素因子除完，看看最后值是否等于1即可。

过程详见代码：

class Solution {
public:
bool isUgly(int num) {
int last = num;
while(num > 0)
{
if(num % 2 == 0) num = num / 2;
if(num % 3 == 0) num = num / 3;
if(num % 5 == 0) num = num / 5;
if(last == num) break;
last = num;
}
return num == 1;
}
};