Permutations of Integer Array, return List of ArrayLists

PermutationsIntegerArray.java

public class Solution {
    public List<List<Integer>> permute(int[] num) {
        boolean[] used = new boolean[num.length];
        for (int i = 0; i < used.length; i ++) used[i] = false;
        
        List<List<Integer>> output = new ArrayList<List<Integer>>();
        ArrayList<Integer> temp = new ArrayList<Integer>();
       
        permuteHelper(num, 0, used, output, temp);
        
        return output;
        
    }
    
    public void permuteHelper(int[] num, int level, boolean[] used, List<List<Integer>> output, ArrayList<Integer> temp){
        
        if (level == num.length){
            output.add(new ArrayList<Integer>(temp));
        }
        else{
            
            for (int i = 0; i < num.length; i++){
                if (!used[i]){
                    temp.add(num[i]);
                    used[i] = true;
                    permuteHelper(num, level+1, used, output, temp);
                    used[i] = false;
                    temp.remove(temp.size()-1);
                    
                }
            }
            
        }
        
    }
}


//Testing:

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

public class Solution {
  
  public static void main(String[] args)
  {
    int array[]={1,2,3,4,5,6};
    List<List<Integer>> listList = permute(array);
      
      for (List<Integer> list : listList){
        for (Integer i : list){
          System.out.print(i + " ");
        }
        System.out.println();
      }
	
 
  }
  
    public static List<List<Integer>> permute(int[] num) {
        boolean[] used = new boolean[num.length];
        for (int i = 0; i < used.length; i ++) used[i] = false;

        List<List<Integer>> output = new ArrayList<List<Integer>>();
        ArrayList<Integer> temp = new ArrayList<Integer>();

        permuteHelper(num, 0, used, output, temp);

        return output;

    }

    public static void permuteHelper(int[] num, int level, boolean[] used, List<List<Integer>> output, ArrayList<Integer> temp){

        if (level == num.length){
            output.add(new ArrayList<Integer>(temp));
        }
        else{

            for (int i = 0; i < num.length; i++){
                if (!used[i]){
                    temp.add(num[i]);
                    used[i] = true;
                    permuteHelper(num, level+1, used, output, temp);
                    used[i] = false;
                    temp.remove(temp.size()-1);

                }
            }

        }

    }
}