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.

思路：
如果num为1直接返回true；如果num小于0直接返回false。循环条件为num>=2，分别判断是否能整除2、3、5，若能整除就计算；如果不能直接返回false。如果最后跳出循环，肯定为true。

代码：

class Solution {public:    bool isUgly(int num) {        if(num==1){//如果num为1直接返回true            return true;        }        if(num<=0){//如果num小于0直接返回false            return false;        }        while(num>=2){            if(num%2==0){//分别判断是否能整除2、3、5，若能整除就计算                num/=2;            }            else if(num%3==0){                num/=3;            }            else if(num%5==0){                num/=5;            }            else{//不能直接返回false                return false;            }        }        return true;//如果最后跳出循环，肯定为true    }};