Longest Repeating Character Replacement

Problem Given a string of uppercase letters and an integer k, find the length of the longest substring you can make consist of a single repeated letter by replacing at most k characters.

Input / Output

• Input: string s, integer k.
• Output: the length of the longest achievable single-letter substring.

Constraints

• 1 ≤ |s| ≤ 10^5; k ≥ 0.

Example

• s = "AABABBA", k = 1 → 4.
• s = "ABAB", k = 2 → 4.