# 5. Longest Palindromic Substring

## Medium

***

Given a string `s`, return _the longest palindromic substring_ in `s`.

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**Example 1:**

```
Input: s = "babad"
Output: "bab"
Explanation: "aba" is also a valid answer.
```

**Example 2:**

```
Input: s = "cbbd"
Output: "bb"
```

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**Constraints:**

* `1 <= s.length <= 1000`
* `s` consist of only digits and English letters.
