Permutation of a string

http://www.programmerinterview.com/index.php/recursion/permutations-of-a-string/

import java.util.HashSet;

import java.util.Set;

 

/**

 * Java Program to find all permutations of a String

 * @author pankaj

 *

 */

public class StringHelper {

    public static Set<String> permutationFinder(String str) {

        Set<String> perm = new HashSet<String>();

        //Handling error scenarios

        if (str == null) {

            return null;

        } else if (str.length() == 0) {

            perm.add("");

            return perm;

        }

        char initial = str.charAt(0); // first character

        String rem = str.substring(1); // Full string without first character

        Set<String> words = permutationFinder(rem);

        for (String strNew : words) {

            for (int i = 0;i<=strNew.length();i++){

                perm.add(charInsert(strNew, initial, i));

            }

        }

        return perm;

    }

 

    public static String charInsert(String str, char c, int j) {

        String begin = str.substring(0, j);

        String end = str.substring(j);

        return begin + c + end;

    }

 

    public static void main(String[] args) {

        String s = "AAC";

        String s1 = "ABC";

        String s2 = "ABCD";

        System.out.println("\nPermutations for " + s + " are: \n" + permutationFinder(s));

        System.out.println("\nPermutations for " + s1 + " are: \n" + permutationFinder(s1));

        System.out.println("\nPermutations for " + s2 + " are: \n" + permutationFinder(s2));

    }

}

 

source http://www.journaldev.com/526/java-program-to-find-all-permutations-of-a-string