Project Notes

Longest Palindromic Substring

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Description

tab: English
 
<p>Given a string <code>s</code>, return <em>the longest</em> <span data-keyword="palindromic-string"><em>palindromic</em></span> <span data-keyword="substring-nonempty"><em>substring</em></span> in <code>s</code>.</p>
 
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
 
<pre>
<strong>Input:</strong> s = &quot;babad&quot;
<strong>Output:</strong> &quot;bab&quot;
<strong>Explanation:</strong> &quot;aba&quot; is also a valid answer.
</pre>
 
<p><strong class="example">Example 2:</strong></p>
 
<pre>
<strong>Input:</strong> s = &quot;cbbd&quot;
<strong>Output:</strong> &quot;bb&quot;
</pre>
 
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>
 
<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> consist of only digits and English letters.</li>
</ul>
 
 
 
> [!tip]- Hint 1
> 
> How can we reuse a previously computed palindrome to compute a larger palindrome?
 
> [!tip]- Hint 2
> 
> If “aba” is a palindrome, is “xabax” a palindrome? Similarly is “xabay” a palindrome?
 
> [!tip]- Hint 3
> 
> Complexity based hint:</br>

If we use brute-force and check whether for every start and end position a substring is a palindrome we have O(n^2) start - end pairs and O(n) palindromic checks. Can we reduce the time for palindromic checks to O(1) by reusing some previous computation.
 
 
---
 
[submissions](https://leetcode.com/problems/longest-palindromic-substring/submissions/) | [solutions](https://leetcode.com/problems/longest-palindromic-substring/solutions/)
 
 
tab: 中文
 
<p>给你一个字符串 <code>s</code>，找到 <code>s</code> 中最长的 <span data-keyword="palindromic-string">回文</span> <span data-keyword="substring-nonempty">子串</span>。</p>
 
<p>&nbsp;</p>
 
<p><strong>示例 1：</strong></p>
 
<pre>
<strong>输入：</strong>s = "babad"
<strong>输出：</strong>"bab"
<strong>解释：</strong>"aba" 同样是符合题意的答案。
</pre>
 
<p><strong>示例 2：</strong></p>
 
<pre>
<strong>输入：</strong>s = "cbbd"
<strong>输出：</strong>"bb"
</pre>
 
<p>&nbsp;</p>
 
<p><strong>提示：</strong></p>
 
<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> 仅由数字和英文字母组成</li>
</ul>
 
 
 
> [!tip]- 提示 1
> 
> How can we reuse a previously computed palindrome to compute a larger palindrome?
 
> [!tip]- 提示 2
> 
> If “aba” is a palindrome, is “xabax” a palindrome? Similarly is “xabay” a palindrome?
 
> [!tip]- 提示 3
> 
> Complexity based hint:</br>

If we use brute-force and check whether for every start and end position a substring is a palindrome we have O(n^2) start - end pairs and O(n) palindromic checks. Can we reduce the time for palindromic checks to O(1) by reusing some previous computation.
 
 
---
 
[提交记录](https://leetcode.cn/problems/longest-palindromic-substring/submissions/) | [题解](https://leetcode.cn/problems/longest-palindromic-substring/solution/)

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