ReturnSubsequence.java

/*
This program will return all the subsequences of the input string in a string array;
Sample Input:
abc
Sample Output:
"" ( Empty String )
c
b
bc
a
ac
ab
abc

 */

import java.util.Scanner;

public class ReturnSubsequence {
    /*
    Main function will accept the given string and implement return subsequences function
     */
    public static void main(String[] args) {
        System.out.println("Enter String: ");
        Scanner s=new Scanner(System.in);
        String givenString=s.next(); //given string
        String[] subsequence=returnSubsequence(givenString); //calling returnSubsequence() function
        System.out.println("Subsequences : ");
        for(int i=0;i<subsequence.length;i++) //print the given array of subsequences
        {
            System.out.println(subsequence[i]);
        }
    }
     /*
     Recursive function to return Subsequences
      */
    private static String[] returnSubsequence(String givenString) {
        if(givenString.length()==0) // If string is empty we will create an array of size=1 and insert "" (Empty string) in it
        {
           String[] ans=new String[1];
           ans[0]="";
           return  ans;

        }
        String[] SmallAns=returnSubsequence(givenString.substring(1)); //recursive call to get subsequences of substring starting from index position=1

        String[] ans=new String[2*SmallAns.length];// Our answer will be an array off string of size=2*SmallAns
        int i=0;
        for (;i<SmallAns.length;i++)
        {
            ans[i]=SmallAns[i]; //Copying all the strings present in SmallAns to ans string array
        }
        for (int k=0;k<SmallAns.length;k++)
        {
            ans[k+SmallAns.length]=givenString.charAt(0)+SmallAns[k]; // Insert character at index=0 of the given substring in front of every string in SmallAns
        }
        return ans;
    }
}