Longest Repeating Character Replacement

• https://leetcode.com/problems/longest-repeating-character-replacement/
• Maintaining the properties of the window.

counter = Counter()
w = max_len = start = max_count = 0
for c in s:
    w += 1
    counter[c] += 1
    if max_count < counter[c]:
        max_count = counter[c]
    if w - max_count > k:
        counter[s[start]] -= 1
        start += 1
        w -= 1
    else:
        max_len = w if max_len < w else max_len
return max_len