leetcode 263. Ugly Number丑数

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.

思路：

  只需要循环除以2，3，5，如果最后的结果是1，则返回true；如果最后的结果不是1，则存在其他的质因数，返回false。

代码：

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