LeetCode 263. Ugly Number

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本文介绍了一种用于检查给定整数是否为丑数的递归算法。丑数定义为只包含质因数2、3、5的正整数，其中1也被视为丑数。算法通过递归除以可能的质因数来验证输入数字是否符合丑数的定义。

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.

Do it recursively.

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