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 that 1 is typically treated as an ugly number.

题意分析：
我们把只包含因子2、3和5的数称作丑数（Ugly Number）。例如6、8都是丑数，但14不是，因为它包含因子7。习惯上我们把1当做是第一个丑数。

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class Solution {
public:
    bool (int num) {
        while (num > 0 && num % 2 == 0)
            num /= 2;
        while (num > 0 && num % 3 == 0)
            num /= 3;
        while (num > 0 && num % 5 == 0)
            num /= 5;
        return num == 1;
    }
};