Project Notes

Ugly Number II

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Description

tab: English
 
<p>An <strong>ugly number</strong> is a positive integer whose prime factors are limited to <code>2</code>, <code>3</code>, and <code>5</code>.</p>
 
<p>Given an integer <code>n</code>, return <em>the</em> <code>n<sup>th</sup></code> <em><strong>ugly number</strong></em>.</p>
 
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
 
<pre>
<strong>Input:</strong> n = 10
<strong>Output:</strong> 12
<strong>Explanation:</strong> [1, 2, 3, 4, 5, 6, 8, 9, 10, 12] is the sequence of the first 10 ugly numbers.
</pre>
 
<p><strong class="example">Example 2:</strong></p>
 
<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 1
<strong>Explanation:</strong> 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.
</pre>
 
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>
 
<ul>
	<li><code>1 &lt;= n &lt;= 1690</code></li>
</ul>
 
 
 
> [!tip]- Hint 1
> 
> The naive approach is to call <code>isUgly</code> for every number until you reach the n<sup>th</sup> one. Most numbers are <i>not</i> ugly. Try to focus your effort on generating only the ugly ones.
 
> [!tip]- Hint 2
> 
> An ugly number must be multiplied by either 2, 3, or 5 from a smaller ugly number.
 
> [!tip]- Hint 3
> 
> The key is how to maintain the order of the ugly numbers. Try a similar approach of merging from three sorted lists: L<sub>1</sub>, L<sub>2</sub>, and L<sub>3</sub>.
 
> [!tip]- Hint 4
> 
> Assume you have U<sub>k</sub>, the k<sup>th</sup> ugly number. Then U<sub>k+1</sub> must be Min(L<sub>1</sub> * 2, L<sub>2</sub> * 3, L<sub>3</sub> * 5).
 
 
---
 
[submissions](https://leetcode.com/problems/ugly-number-ii/submissions/) | [solutions](https://leetcode.com/problems/ugly-number-ii/solutions/)
 
 
tab: 中文
 
<p>给你一个整数 <code>n</code> ，请你找出并返回第 <code>n</code> 个 <strong>丑数</strong> 。</p>
 
<p><strong>丑数 </strong>就是质因子只包含&nbsp;<code>2</code>、<code>3</code> 和&nbsp;<code>5</code>&nbsp;的正整数。</p>
 
<p>&nbsp;</p>
 
<p><strong>示例 1：</strong></p>
 
<pre>
<strong>输入：</strong>n = 10
<strong>输出：</strong>12
<strong>解释：</strong>[1, 2, 3, 4, 5, 6, 8, 9, 10, 12] 是由前 10 个丑数组成的序列。
</pre>
 
<p><strong>示例 2：</strong></p>
 
<pre>
<strong>输入：</strong>n = 1
<strong>输出：</strong>1
<strong>解释：</strong>1 通常被视为丑数。
</pre>
 
<p>&nbsp;</p>
 
<p><strong>提示：</strong></p>
 
<ul>
	<li><code>1 &lt;= n &lt;= 1690</code></li>
</ul>
 
 
 
> [!tip]- 提示 1
> 
> The naive approach is to call <code>isUgly</code> for every number until you reach the n<sup>th</sup> one. Most numbers are <i>not</i> ugly. Try to focus your effort on generating only the ugly ones.
 
> [!tip]- 提示 2
> 
> An ugly number must be multiplied by either 2, 3, or 5 from a smaller ugly number.
 
> [!tip]- 提示 3
> 
> The key is how to maintain the order of the ugly numbers. Try a similar approach of merging from three sorted lists: L<sub>1</sub>, L<sub>2</sub>, and L<sub>3</sub>.
 
> [!tip]- 提示 4
> 
> Assume you have U<sub>k</sub>, the k<sup>th</sup> ugly number. Then U<sub>k+1</sub> must be Min(L<sub>1</sub> * 2, L<sub>2</sub> * 3, L<sub>3</sub> * 5).
 
 
---
 
[提交记录](https://leetcode.cn/problems/ugly-number-ii/submissions/) | [题解](https://leetcode.cn/problems/ugly-number-ii/solution/)

Solutions & Notes

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