[LeetCode每日一题]263. Ugly Number

题目如下：

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.

Example 1:
Input: 6
Output: true
Explanation: 6 = 2 × 3

Example 2:
Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2

Example 3:
Input: 14
Output: false 
Explanation: 14 is not ugly since it includes another prime factor 7.

Note:
1.1 is typically treated as an ugly number.
2.Input is within the 32-bit signed integer range: [−231,  231 − 1].

263. Ugly Number
定义仅由任意个2，3，5相乘得到的正整数为ugly数，例如12=223是ugly数，45=335是ugly数，1是特殊的ugly数。输入一个正整数，让我们判断它是不是ugly数。
解决这道题，只需不断用2，3，5整除给定的正整数num到不能整除为止，看最后的结果是不是1即可。
实现代码如下：

class Solution {
    public boolean isUgly(int num) {
        if (num < 0) {
            return false;
        }
        while (num > 1 && num % 2.0 == 0) {
            num /= 2;
        }
        while (num > 1 && num % 3.0 == 0) {
            num /= 3;
        }
        while (num > 1 && num % 5.0 == 0) {
            num /= 5;
        }
        return num == 1;
    }
}