leetcode笔记：Ugly Number

一. 题目描述

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.

二. 题目分析

该题的大意是编写一个函数，判断输入的整数是否为丑数。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。题目也提到，习惯上把1也当做是一个丑数。

三. 示例代码

class Solution {
public:
    bool isUgly(int num) {
        if (num < 1) return false;
        if (num == 1) return true;
        else
        {
            while (num > 1)
            {
                if (num % 2 == 0)
                {
                    num /= 2;
                    continue;
                }
                else if (num % 3 == 0)
                {
                    num /= 3;
                    continue;
                }
                else if (num % 5 == 0)
                {
                    num /= 5;
                    continue;
                }
                else return false;
            }
            return true;
        }
    }
};

四. 小结

该题没有过多的边界条件和技巧，找准规律即可。