import java.util.*;
class Main {

    public List<List<Character>> subsets(String s) {
        List<List<Character>> list = new ArrayList<>();
        char [] c = s.toCharArray();
        backtrack(list, new ArrayList<>(), c, 0);
        return list;
    }

    private void backtrack(List<List<Character>> list , List<Character> tempList, char [] cs, int start){
        if(!tempList.isEmpty())
            list.add(new ArrayList<>(tempList));
        for(int i = start; i < cs.length; i++){
            tempList.add(cs[i]);
            backtrack(list, tempList, cs, i + 1);
            tempList.remove(tempList.size() - 1);
        }
    }
    public static void main(String[] args) {
        System.out.println(new Main().subsets("xyz"));
    }
}