/**
 * @param {string} s
 * @param {number} k
 * @return {number}
 */
var characterReplacement = function (s, k) {
  let start = 0;
  let end = 0;
  let map = new Map();
  let mostFreqCharacter = 0;
  let longestLength = 0;

  while (s.length > end) {
    map.has(s[end]) ? map.set(s[end], map.get(s[end]) + 1) : map.set(s[end], 1);

    mostFreqCharacter = Math.max(mostFreqCharacter, map.get(s[end]));

    let remaining = end - start + 1 - mostFreqCharacter;

    if (remaining > k) {
      map.set(s[start], map.get(s[start]) - 1);
      start++;
    }
    longestLength = Math.max(longestLength, end - start + 1);
    end++;
  }
  return longestLength;
};