# 424 Longest Repeating Character Replacement

You are given a string `s` and an integer `k`. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most `k` times.

Return the length of the longest substring containing the same letter you can get after performing the above operations.

Example 1:

``````Input: s = "ABAB", k = 2
Output: 4
Explanation: Replace the two 'A's with two 'B's or vice versa.
``````

Example 2:

``````Input: s = "AABABBA", k = 1
Output: 4
Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.
``````

Constraints:

• `1 <= s.length <= 105`
• `s` consists of only uppercase English letters.
• `0 <= k <= s.length`
 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 `````` ``````class Solution: def characterReplacement(self, s: str, k: int) -> int: win_start = 0 max_len = 0 count_map = defaultdict(int) # char count within the current window max_count = 0 for win_end, c in enumerate(s): count_map[c] += 1 max_count = max(max_count, count_map[c]) if win_end - win_start + 1 - max_count > k: count_map[s[win_start]] -= 1 win_start += 1 max_len = max(max_len, win_end - win_start + 1) return max_len``````