longest-repeating-character-replacement.js

/**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. */
/**
 * @param {string} s
 * @param {number} k
 * @return {number}
 */
 var characterReplacement = function(s, k) {
    let start = 0;
    let end = 0;
    let maxCount = 0;
    let res = 0;
    let map = {};
    
    for (let i = 0; i < s.length; i++) {
      let ch = s[i];
      if (!(ch in map)) {
        map[ch] = 0;
      }
      map[ch]++;
      maxCount = Math.max(map[ch], maxCount);
      
      
      if (i - start + 1 - maxCount > k) {
        map[s[start]]--;
        start++
      }
      
      res = Math.max(res, i - start + 1);    
    }
    
    return res;
      
  };