Create ArrayList from permutations Java

Question

I hope this isn't a stupid question but I took the code below from another post. It just generates all permutations of a string. What I'd like to do is just modify it so all the permutations are added to an arraylist but I'm having some trouble finding what is hopefully the simple obvious solution. Can someone give this a quick look and explain what I'm doing wrong? I just want to take the permutations of a string and create an array list, that's all.

public class UserInput {

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    System.out.println("Enter Word: ");
    List<String> inputList = new ArrayList<String>();
    String input = scan.next();
    permutation(input);

            //Error occurs here
    inputList.addAll(permutation(input));

}

public  static void permutation(String str) { 
    permutation("", str);
 }

 private static void permutation(String prefix, String str) {   
    int n = str.length();
    if (n == 0) System.out.println(prefix);
    else {
        for (int i = 0; i < n; i++)
           permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i+1, n));
    }
}

}

arynaq · Accepted Answer · 2013-06-06 21:07:08Z

Permutation has no return type, it is a void method, you are putting it in a list which only accepts objects of type String. You can modify it so once the recursion reaches the lowest level it adds itself to the list like so:

public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    System.out.println("Enter Word: ");
    List<String> inputList = new ArrayList<String>();
    String input = scan.next();
    permutation(input, inputList);

    System.out.println(inputList);

}

public static void permutation(String str, List<String> result) {
    permutation("", str, result);
}

private static void permutation(String prefix, String str,
        List<String> container) {
    int n = str.length();
    if (n == 0) {
        container.add(prefix);
    } else {
        for (int i = 0; i < n; i++)
            permutation(prefix + str.charAt(i),
                    str.substring(0, i) + str.substring(i + 1, n),
                    container);
    }
}

For "Hei"

[Hei, Hie, eHi, eiH, iHe, ieH]

user2461391 · Accepted Answer · 2013-06-06 21:11:05Z

Instead of printing the permutation out, you can add it to the list.

import java.util.List;
import java.util.ArrayList;
import java.util.Scanner;

public class UserInput {
private static List<String> inputList;
public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    System.out.println("Enter Word: ");
    inputList = new ArrayList<>();
    String input = scan.next();
    permutation(input);

   System.out.println(inputList.toString());

}

public  static void permutation(String str) { 
    permutation("", str);
 }

 private static void permutation(String prefix, String str) {   
    int n = str.length();
    if (n == 0) inputList.add(prefix);
    else {
        for (int i = 0; i < n; i++)
           permutation(prefix + str.charAt(i), str.substring(0, i) + str.substring(i+1, n));
    }
}
}

jlordo · Accepted Answer · 2013-06-06 21:09:51Z

-1

permutation(input) returns void, while inputList.addAll() expects Collection<String>.

edited Jun 6, 2013 at 21:09

jlordo

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answered Jun 6, 2013 at 21:07

Shamim Hafiz - MSFT

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