# 1371. Find the Longest Substring Containing Vowels in Even Counts

<https://leetcode.com/problems/find-the-longest-substring-containing-vowels-in-even-counts>

## Description

Given the string `s`, return the size of the longest substring containing each vowel an even number of times. That is, 'a', 'e', 'i', 'o', and 'u' must appear an even number of times.

**Example 1:**

```
**Input:** s = "eleetminicoworoep"
**Output:** 13
**Explanation:** The longest substring is "leetminicowor" which contains two each of the vowels: **e**, **i** and **o** and zero of the vowels: **a** and **u**.
```

**Example 2:**

```
**Input:** s = "leetcodeisgreat"
**Output:** 5
**Explanation:** The longest substring is "leetc" which contains two e's.
```

**Example 3:**

```
**Input:** s = "bcbcbc"
**Output:** 6
**Explanation:** In this case, the given string "bcbcbc" is the longest because all vowels: **a**, **e**, **i**, **o** and **u** appear zero times.
```

**Constraints:**

* `1 <= s.length <= 5 x 10^5`
* `s` contains only lowercase English letters.

## ac

```java
```


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