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# 1624. Largest Substring Between Two Equal Characters

<https://leetcode.com/problems/largest-substring-between-two-equal-characters>

## Description

Given a string `s`, return *the length of the longest substring between two equal characters, excluding the two characters.* If there is no such substring return `-1`.

A **substring** is a contiguous sequence of characters within a string.

**Example 1:**

```
**Input:** s = "aa"
**Output:** 0
**Explanation:** The optimal substring here is an empty substring between the two 'a's.
```

**Example 2:**

```
**Input:** s = "abca"
**Output:** 2
**Explanation:** The optimal substring here is "bc".
```

**Example 3:**

```
**Input:** s = "cbzxy"
**Output:** -1
**Explanation:** There are no characters that appear twice in s.
```

**Example 4:**

```
**Input:** s = "cabbac"
**Output:** 4
**Explanation:** The optimal substring here is "abba". Other non-optimal substrings include "bb" and "".
```

**Constraints:**

* `1 <= s.length <= 300`
* `s` contains only lowercase English letters.

## ac

```java
```