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424. Longest Repeating Character Replacement

Difficulty Topics

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.

 

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

longest-repeating-character-replacement.py
class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
        counter = Counter()
        i = maxCount = res = 0

        for j, x in enumerate(s):
            counter[x] += 1
            maxCount = max(maxCount, counter[x])

            while j - i + 1 - maxCount > k:
                counter[s[i]] -= 1
                i += 1

            res = max(res, j - i + 1)

        return res