Longest repeating character replacement

Problem statement

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.

Using sliding window technique

/**
 * @param {string} s
 * @param {number} k
 * @return {number}
 */
var characterReplacement = function(s, k) {
    let maxLen = 0;
    let left = 0;
    let maxCount = 0;

    const freq = {};

    for (let right = 0; right < s.length; right++) {
        const char = s[right];
        freq[char] = (freq[char] || 0) + 1;

        maxCount = Math.max(maxCount, freq[char]);

        while ((right - left + 1) - maxCount > k) {
            freq[s[left]]--;
            left++;
        }

        maxLen = Math.max(maxLen, right - left + 1);
    }

    return maxLen;
};