424. Longest Repeating Character Replacement

Description

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.

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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

Solution

This solution is from Neetcode

def characterReplacement(self, s: str, k: int) -> int:
        l = 0 
        count = {} 
        maxf = 0 
        res = 0 

        for r in range(len(s)):
            count[s[r]] = 1 + count.get(s[r],0)
            maxf = max(maxf,count[s[r]])
            if ((r-l+1) - maxf) > k:
                count[s[l]] -= 1
                l += 1
            res = max(res, r - l + 1)
        return res