263. Ugly Number 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.

Example 1:

Input: 6
Output: true
Explanation: 6 = 2 × 3

Example 2:

Input: 8
Output: true
Explanation: 8 = 2 × 2 × 2

Example 3:

Input: 14
Output: false 
Explanation: 14 is not ugly since it includes another prime factor 7.

Note:

1. 1 is typically treated as an ugly number.
2. Input is within the 32-bit signed integer range: [−2³¹,  2³¹ − 1]. 263. Ugly Number

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本题要判断一个数是否是丑数，丑数的定义是素因子只有2,3,5，简单想法就是不断的除这些数，如果最后结果是1，则说明素因子只有2,3,5，否则还有其他素因子。 完整代码如下：

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

本代码提交AC，用时3MS。

二刷：

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

本代码提交AC，用时0MS。