Longest Repeating Character Replacement

You may change at most `k` characters of the uppercase string `s` to any other uppercase letter. Return the length of the longest substring that can be made of a single repeated letter. **Example 1:** ``` Input: s = "ABAB", k = 2 Output: 4 ``` **Example 2:** ``` Input: s = "AABABBA", k = 1 Output: 4 ``` **Example 3:** ``` Input: s = "AAAA", k = 0 Output: 4 ```