[leetcode]53 Ugly Number

題目連結：https://leetcode.com/problems/ugly-number/

Runtime：8ms

1、問題

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.

2、分析

很顯然，num<=0 的所有情況都應該傳回false，因為因子中有負數，不單單包含2， 3， 5。其次做因子判斷，如果數字不能被2、3、5整除，那麼傳回false，否則傳回true啦。

3、小結

沒有進行分析就直接寫代碼是不對滴：

1、沒考慮負數

2、while條件不正确：1 < num

3、精簡代碼：不用對1單獨判斷

4、實作

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

5、反思

思考後下筆，良策！