> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/1682-longest-palindromic-subsequence-ii.md).

# 1682. Longest Palindromic Subsequence II

<https://leetcode.com/problems/longest-palindromic-subsequence-ii>

## Description

A subsequence of a string `s` is considered a **good palindromic subsequence** if:

* It is a subsequence of `s`.
* It is a palindrome (has the same value if reversed).
* It has an **even** length.
* No two consecutive characters are equal, except the two middle ones.

For example, if `s = "abcabcabb"`, then `"abba"` is considered a **good palindromic subsequence**, while `"bcb"` (not even length) and `"bbbb"` (has equal consecutive characters) are not.

Given a string `s`, return *the **length** of the **longest good palindromic subsequence** in* `s`.

**Example 1:**

```
**Input:** s = "bbabab"
**Output:** 4
**Explanation:** The longest good palindromic subsequence of s is "baab".
```

**Example 2:**

```
**Input:** s = "dcbccacdb"
**Output:** 4
**Explanation:** The longest good palindromic subsequence of s is "dccd".
```

**Constraints:**

* `1 <= s.length <= 250`
* `s` consists of lowercase English letters.

## ac

```java
```