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 balancedif 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

• scontains only 'Q', 'W', 'E' and 'R'.

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