Sliding Window: longest substring with same letters

longestSubstringWithSameLetter.js

/*
Steps:

1. We'll iterate through the array
2. We'll create a hashmap to remember the occurence for each char
3. We'll also remember the most repeated char in the sliding window
4. If we removed the most repeated char from the sliding window and the left chars to replace with the most repeated char is more than K, we'll shrink the window
5. We'll remember the length of the sliding window as the one with the longest substring with the same letter
*/

const longestSubstringWithSameLetters = (arr, K) => {
  let windowStart = 0,
    maxLength = 0,
    mostRepeatedChar = 0,
    hashMap = {};

  for (let windowEnd = 0; windowEnd < arr.length; windowEnd++) {
    const rightChar = arr[windowEnd]
    // Remember the char occurrence
    hashMap[rightChar] = (hashMap[rightChar] || 0) + 1
    
    // Remeber the most repeated character in the current sliding window
    mostRepeatedChar = Math.max(mostRepeatedChar, hashMap[rightChar])
    
    // If after removing the most repeated chars from the sliding window,
    // the count of the chars to be replaced with the char of the most 
    // repeated char is more than K, slide the first element out
    // E.g, in `aabcc` the most repeated char is `a`
    // After removing `a`, we get `bcc`. `bcc` is greater than K
    // if `k` is 2. So, we shrink the window now
    if ((windowEnd - windowStart + 1 - mostRepeatedChar) > K) {
      // We could remove the character from hasMap but it didn't 
      // change the output to me
      // hashMap[arr[windowStart]] -= 1
      windowStart += 1
    }
    
    // Set the longest substring by comparing the current window size to the
    // previous window size
    maxLength = Math.max(maxLength, windowEnd - windowStart + 1)
  }
  
  return maxLength
};

longestSubstringWithSameLetters('aabccbb', 2) // 5
longestSubstringWithSameLetters('abbcb', 1) // 4
longestSubstringWithSameLetters('abccde', 1) // 3