public int characterReplacement(String s, int k) {
int start = 0, end = 0, maxCount = 0, maxLen = 0;
int[] map = new int[256];
while (end < s.length()) {
maxCount = Math.max(maxCount, map[s.charAt(end)]);
if (end - start - maxCount > k) {
maxLen = Math.max(maxLen, end - start);