Question

Write a program to print all permutations of String?

Answer 1

This is a tricky question and we need to use recursion to find all the permutations of a String, for example “AAB” permutations will be “AAB”, “ABA” and “BAA”.

We also need to use Set to make sure there are no duplicate values.

Check this post for complete program to find all permutations of String.
 

import java.util.HashSet;

import java.util.Set;

 

public class StringExample

{

    public static void main(String[] args)

    {

        System.out.println(getPermutations("ABC"));

 

        //Prints

        //[ACB, BCA, ABC, CBA, BAC, CAB]

    }

 

    public static Set<String> getPermutations(String string)

    {

        //All permutations

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

         

        // invalid strings

        if (string == null || string.length() == 0)

        {

            permutationsSet.add("");

        }

        else

        {

            //First character in String

            char initial = string.charAt(0);

             

            //Full string without first character

            String rem = string.substring(1);

             

            //Recursive call

            Set<String> wordSet = getPermutations(rem);

             

            for (String word : wordSet) {

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

                    permutationsSet.add(charInsertAt(word, initial, i));

                }

            }

        }

        return permutationsSet;

    }

 

    public static String charInsertAt(String str, char c, int position)

    {

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

        String end = str.substring(position);

        return begin + c + end;

    }

}