ЯсноПонятно24

public class App {
    public static void main(String[] args) {
        String str = "qweqrty";
        System.out.println(getLongestLength(str)); // Output: 6
    }

    public static int getLongestLength(String s) {
        int n = s.length();
        int res = 0;
        int[] lastIndex = new int[256];
        Arrays.fill(lastIndex, -1);
        int i = 0;

        for (int j = 0; j < n; j++) {
            i = Math.max(i, lastIndex[s.charAt(j)] + 1);
            res = Math.max(res, j - i + 1);
            lastIndex[s.charAt(j)] = j;
        }

        return res;
    }
}