263. Ugly Number

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:

1. 1 is typically treated as an ugly number.

1. Input is within the 32-bit signed integer range.

题意：

判断一个数是否为丑数。丑数：质因数只可能为2,3,5的数

思路：

先一直除以2，直到不能除尽，再除以3，直到不能除尽，再除以5直到不能除尽，最后如果是1，就是丑数，否则就不是。

代码：

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