Permutation algorithm for array of integers in Java

Question

I have a working example to generate all char permutations in a String as below:

static ArrayList permutations(String s) {
        if (s == nul         


        

Answer 1

By adding a TreeSet it removes duplicates and sorts the permutations.

---

package permutations;

import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.TreeSet;


public class Permutations {


public static void main(String args[])
{
    Scanner scanner = new Scanner(new InputStreamReader(System.in));
    System.out.println("This application accepts input of a string and creates a list of all     possible permutations\n\r");

    System.out.println("Please Enter a string of characters");
    String input = scanner.nextLine();

    String[] elements = input.split("");
    Permutations g = new Permutations();

    ArrayList permutations = g.generatePermutations(elements);

    TreeSet ts = new TreeSet();
    for ( String s : permutations)
    {
        //System.out.println(s);
        ts.add(s);
    }
    System.out.println("List of all possible permutations");
    System.out.println(ts);

}

private ArrayList generatePermutations( String[] elements )
{
    ArrayList permutations = new ArrayList();
    if ( elements.length == 2 )
    {

        String x1 = elements[0]  + elements[1]; 
        String x2 = elements[1]  + elements[0];  
        permutations.add(x1);
        permutations.add(x2);

    }
    else {
        for (  int i = 0 ; i < elements.length  ; i++)
        {
            String[] elements2 = new String[elements.length -1];
            int kalo = 0;
            for( int j =0 ; j< elements2.length ; j++ )
            {
                if( i == j)
                {
                    kalo = 1;
                }
                elements2[j] = elements[j+kalo];
            }
            ArrayList k2 = generatePermutations(elements2);
            for( String x : k2 )
            {
                String s = elements[i]+x;
                permutations.add(s);
            }
        }
    }

    return permutations;
    }
}