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：

将num一直除以 2,3,5，一直到没法除为止，判断结果是否为1。

bool isUgly(int num)
 {
        if(num<=0) return false;
        if(num == 1) return true;    
    while(num % 2 == 0)num/=2;
    while(num % 3 == 0)num/=3;
    while(num % 5 == 0)num/=5;
    if(num!=1) return false;
    return true;    
 }

[leetcode-263-Ugly Number]