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.

Solution：Math

思路： 如果能整除一直除2，3，5，看最后是否等于1
Time Complexity: O(N) Space Complexity: O(1)

Solution Code：

class Solution {
    public boolean isUgly(int num) {
        if(num < 1) return false;
        
        int factors[] = new int[]{2, 3, 5};
        for(int f: factors) {
            while(num % f == 0) {
                num /= f;
            }
        }
        return num == 1;
    }
}