ЯсноПонятно24

import java.util.HashSet;

public class App {
    public static int getLongestLength(String str) {
        int maxLength = 0;
        int start = 0;
        HashSet<Character> set = new HashSet<>();

        for (int end = 0; end < str.length(); end++) {
            char c = str.charAt(end);
            while (set.contains(c)) {
                set.remove(str.charAt(start));
                start++;
            }
            set.add(c);
            maxLength = Math.max(maxLength, end - start + 1);
        }

        return maxLength;
    }

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