SubsequenceRec.java

import java.util.*;
public class SubsequenceRec{
    public static void main(String[] args){
        // System.out.println(subseqAsciiRet("", "abc"));
        subseqAscii("", "abc");
    }

    static void subseq(String p, String up){
        if(up.isEmpty()){
            System.out.println(p);
            return;
        }

        char ch = up.charAt(0);
        subseq(p + ch, up.substring(1));
        subseq(p, up.substring(1));
    }

    static ArrayList<String> subseqRet(String p, String up){
        
        if(up.isEmpty()){
            ArrayList<String> list = new ArrayList<>();
            list.add(p);
            return list;
        }

        char ch = up.charAt(0);
        ArrayList<String> left = subseqRet(p + ch, up.substring(1));
        ArrayList<String> right = subseqRet(p, up.substring(1));

        left.addAll(right);
        return left;
    }

    static ArrayList<String> subseqAsciiRet(String p, String up){
        
        if(up.isEmpty()){
            ArrayList<String> list = new ArrayList<>();
            list.add(p);
            return list;
        }

        char ch = up.charAt(0);
        ArrayList<String> first = subseqAsciiRet(p + (ch + 0), up.substring(1));
        ArrayList<String> second = subseqAsciiRet(p, up.substring(1));
        // ArrayList<String> third = subseqAsciiRet(p + (ch + 0), up.substring(1));


        first.addAll(second);
        // first.addAll(third);

        return first;
    }

    static void subseqAscii(String p, String up){
        if(up.isEmpty()){
            System.out.println(p);
            return;
        }

        char ch = up.charAt(0);
        subseqAscii(p + (ch + 0), up.substring(1));
        subseqAscii(p, up.substring(1));
    }
}