LC 424. Longest Repeating Character Replacement

function characterReplacement(s: string, k: number): number {
  let answer = 0
  let freqHash = {}
  let maxFreq = 0
  let leftPointer = 0
  for (let i = 0; i < s.length; i++) {
    freqHash[s[i]] = freqHash[s[i]] ? freqHash[s[i]] + 1 : 1
    maxFreq = Math.max(maxFreq, freqHash[s[i]])
    if (i + 1 - leftPointer - maxFreq > k) {
      freqHash[s[leftPointer]]--
      leftPointer++
    }
    answer = Math.max(answer, i + 1 - leftPointer)
  }
  return answer
}