luzhipeng 48bc053 May 18, 2019
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## 题目地址

https://leetcode.com/problems/ugly-number/description/

## 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.

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

## 思路

while(num % 2 === 0)   num = num / 2;
while(num % 3 === 0)   num = num / 3;
while(num % 5 === 0)   num = num / 5;

return num === 1;

• 数论
• 因数分解

## 代码

/*
* @lc app=leetcode id=263 lang=javascript
*
* [263] Ugly Number
*/
/**
* @param {number} num
* @return {boolean}
*/
var isUgly = function(num) {
// TAG: 数论
if (num <= 0) return false;
if (num === 1) return true;

const list = [2, 3, 5];

if (list.includes(num)) return true;

for (let i of list) {
if (num % i === 0) return isUgly(Math.floor(num / i));
}
return false;
};
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