Max Repeating Characters

Hi All,

I’ve seen a decent amount of questions regarding only keeping the maximum of the repeating character counts. I do understand we do this because it’s the best we can do in the solution, my problem is that the conditional statement no longer makes sense to me.

public static int findLength(String str, int k) {
    int windowStart = 0, maxLength = 0, maxRepeatLetterCount = 0;
    Map<Character, Integer> letterFrequencyMap = new HashMap<>();
    // try to extend the range [windowStart, windowEnd]
    for (int windowEnd = 0; windowEnd < str.length(); windowEnd++) {
      char rightChar = str.charAt(windowEnd);
      letterFrequencyMap.put(rightChar, letterFrequencyMap.getOrDefault(rightChar, 0) + 1);
      maxRepeatLetterCount = Math.max(maxRepeatLetterCount, letterFrequencyMap.get(rightChar));

      // current window size is from windowStart to windowEnd, overall we have a letter which is
      // repeating 'maxRepeatLetterCount' times, this means we can have a window which has one letter 
      // repeating 'maxRepeatLetterCount' times and the remaining letters we should replace.
      // if the remaining letters are more than 'k', it is the time to shrink the window as we
      // are not allowed to replace more than 'k' letters
      if (windowEnd - windowStart + 1 - maxRepeatLetterCount > k) {
        char leftChar = str.charAt(windowStart);
        letterFrequencyMap.put(leftChar, letterFrequencyMap.get(leftChar) - 1);

      maxLength = Math.max(maxLength, windowEnd - windowStart + 1);

    return maxLength;

The line if (windowEnd - windowStart + 1 - maxRepeatLetterCount > k), doesn’t make sense to me because we are comparing against the current window a potential value that does not exist in it.

Please help me with my line of thinking!