# 1234. Replace the Substring for Balanced String

<https://leetcode.com/problems/replace-the-substring-for-balanced-string>

## Description

You are given a string containing only 4 kinds of characters `'Q',` `'W', 'E'` and `'R'`.

A string is said to be **balanced**if each of its characters appears `n/4` times where `n` is the length of the string.

Return the minimum length of the substring that can be replaced with **any** other string of the same length to make the original string `s` **balanced**.

Return 0 if the string is already **balanced**.

**Example 1:**

```
**Input:** s = "QWER"
**Output:** 0
**Explanation:** s is already balanced.
```

**Example 2:**

```
**Input:** s = "QQWE"
**Output:** 1
**Explanation:** We need to replace a 'Q' to 'R', so that "RQWE" (or "QRWE") is balanced.
```

**Example 3:**

```
**Input:** s = "QQQW"
**Output:** 2
**Explanation:** We can replace the first "QQ" to "ER". 
```

**Example 4:**

```
**Input:** s = "QQQQ"
**Output:** 3
**Explanation:** We can replace the last 3 'Q' to make s = "QWER".
```

**Constraints:**

* `1 <= s.length <= 10^5`
* `s.length` is a multiple of `4`
* `s`contains only `'Q'`, `'W'`, `'E'` and `'R'`.

## ac

```java
```