leetcode筆記：Ugly Number

一. 題目描述

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. 題目分析

該題的大意是編寫一個函數，判斷輸入的整數是否為丑數。我們把只包含因子2、3和5的數稱作丑數（Ugly Number）。例如6、8都是丑數，但14不是，因為它包含因子7。題目也提到，習慣上把1也當做是一個丑數。

三. 示例代碼

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. 小結

該題沒有過多的邊界條件和技巧，找准規律即可。