[LeetCode] NO. 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.

[题目解析] 题意要求给定一个数，判断是否为丑数。先来看丑数的定义：质因子只包含2、3或者5的正整数为丑数，即当一个数如14含有另外的质因子7的时候，则不是丑数。根据定义，可以对给定的整数进行2、3或者5因子不断拆解，直到结束，如果不含有别的质因子，则为丑数。

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