424. 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:

Find the longest substring where substring_length - times of most frequent element appeared <= k

public int characterReplacement(String s, int k) {
        if(s == null || s.length() == 0){
            return 0;
        }
        int[] hm = new int[26];
        char[] arr = s.toCharArray();
        int left = 0;
        int max = 0;
        int len = Integer.MIN_VALUE;

        for(int i = 0; i < arr.length; i++){
            max = Math.max(max, ++hm[s.charAt(i) - 'A']);
            while(i - left - max + 1 > k){
                hm[s.charAt(left) - 'A']--;
                left++;
            }
            len = Math.max(len, i - left + 1);

        }
        return len;
    }