PermutationGenerator2.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

public class PermutationGenerator2 {

    private static String inputWithoutC(String input, char c) {
        String inputWithoutC = "";
        char[] temp = input.toCharArray();
        for(char d : temp) {
            if(d !=c ) {
                inputWithoutC += d;
            }
        }
        return inputWithoutC;
    }


    private static ArrayList<String> generatePermutationsOfAString(String input) {
        //null check
        if(input == null) {
            return null;
        }

        ArrayList<String> subPermutations = new ArrayList<String>();
        ArrayList<String> permutations = new ArrayList<String>();

        char[] temp = input.toCharArray();

        //base case: two letters, return each one plus their two permutations
        if(temp.length == 2) {
            permutations.add(String.valueOf(temp[0]));
            permutations.add(String.valueOf(temp[1]));
            permutations.add(String.valueOf(temp[0]) + String.valueOf(temp[1]));
            permutations.add(String.valueOf(temp[1]) + String.valueOf(temp[0]));
            return permutations;
        }

        for(char c : temp) {
            subPermutations = generatePermutationsOfAString(inputWithoutC(input, c));
            /* new line: */ permutations.add(String.valueOf(c));
            for(String s : subPermutations) {
                permutations.add(String.valueOf(c) + s);
            }
        }
        return permutations;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner readUserInput = new Scanner(System.in);
        System.out.println("Enter the source string: ");
        String permuteThis = readUserInput.next();
        System.out.println("\nThe resulting permutations are: ");
        //begin new lines
        ArrayList<String> permutations = generatePermutationsOfAString(permuteThis);
        Collections.sort(permutations);
        //end new lines
        for(String s : permutations) {
            System.out.print(s + "\t");
        }
    }
}