[Swift]LeetCode263. 丑数 | Ugly Number

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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].

编写一个程序判断给定的数是否为丑数。

丑数就是只包含质因数 2, 3, 5 的正整数。

示例 1:

输入: 6
输出: true
解释: 6 = 2 × 3

示例 2:

输入: 8
输出: true
解释: 8 = 2 × 2 × 2

示例 3:

输入: 14
输出: false 
解释: 14 不是丑数，因为它包含了另外一个质因数 7。

说明：

1. 1 是丑数。
2. 输入不会超过 32 位有符号整数的范围: [−231,  231 − 1]。

---

20ms

class Solution {
    func isUgly(_ num: Int) -> Bool {
        if num < 1 {return false}
        var number:Int = num
        while (number % 2 == 0)
        {
            number /= 2
        }
        while (number % 3 == 0)
        {
            number /= 3
        }
        while (number % 5 == 0)
        {
            number /= 5
        }
        return number == 1
    }
}

---

16ms

class Solution {
    func maxDiv(_ num: inout Int, _ div: Int) {
        while (num % div == 0) {
            num = num/div
        }
    }
    
    func isUgly(_ num: Int) -> Bool {
        if(num == 0) {
            return false
        }
        var no = num
        maxDiv(&no, 2)
        maxDiv(&no, 3)
        maxDiv(&no, 5)
        
        if(no == 1){
            return true
        }
        else {
            return false
        }
        
    }
}

---

20ms

class Solution {
    func isUgly(_ num: Int) -> Bool {
        guard num > 0 else {return false}
        var n = num
        
        let divs = [2, 3, 5]
        for d in divs {
            while n % d == 0 {
                n /= d
            }
        }
        return n == 1
    }
}