[LeetCode]: 263: 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.

分析：

说实话，题目根本没有看懂。"prime factors" 这个理解错了。正确的理解是：所有因子都是2或3或5，即这个数是由多个2,3,5相乘组成的

代码：

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