Longest Repeating Character Replacement

Given a string that consists of only uppercase English letters, you can replace any letter in the string with another letter at most k times. Find the length of a longest substring containing all repeating letters you can get after performing the above operations.

Note: Both the string's length and k will not exceed 104.

Example 1:

Input:
s = "ABAB", k = 2

Output:
4

Explanation:
Replace the two 'A's with two 'B's or vice versa.
Example 2:

Input:
s = "AABABBA", k = 1

Output:
4

Explanation:
Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.

Solution

public class Solution {
    public int characterReplacement(String s, int k) {
        int maxLen = 0;

        for(int l = 0; l< 26;l++) {
            char c = (char)('A' + l);
            int i = 0, j = 0, count = 0;

            while(j < s.length()) {
                char cur = s.charAt(j);
                if(cur != c) count ++;

                while(count > k) {
                    if(s.charAt(i) != c) count --;
                    i ++;
                }

                maxLen = Math.max(maxLen, j - i + 1);
                j ++;
            }
        }

        return maxLen;
    }
}