ЯсноПонятно24

import java.util.ArrayList;

public class Main {

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

    public static int findMaxLengthSubsequence(String input) {
        ArrayList<Character> list = new ArrayList<>();
        int maxLength = 0;
        
        for (char c : input.toCharArray()) {
            if (list.contains(c)) {
                maxLength = Math.max(maxLength, list.size());
                int index = list.indexOf(c);
                for (int i = 0; i <= index; i++) {
                    list.remove(0);
                }
            }
            list.add(c);
        }
        
        maxLength = Math.max(maxLength, list.size());
        
        return maxLength;
    }
}