Question

4. [Tests basic knowledge of recursion] Write a recursive static Java method that accepts an array arr of integers argument returns a list of all permutations of these integers.

(A permutation of a sequence of integers is a re-arrangement of the integers. For example, one permutation of 1, 3, 4, 8, 2 is 3, 1, 2, 8, 4.) For this problem, you may assume that the input array contains no duplicate entries. Your method should return an ArrayList of int arrays.

Next, test your method using a main method; the main method should pass in the following array: [1, 5, 4, 2]; then, it should print to the console the resulting list of permutations.

Answer 1

package pk1;

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

public class PermutationofInt {

   public List<List<Integer>> gerPermute(int arr[])
           {
       List<List<Integer>> list=new ArrayList<>();
       permuteEvaluator(list, new ArrayList<>(),arr);
       return list;
           }
   private void permuteEvaluator(List<List<Integer>> list, List<Integer>resultList, int[] arr)
   {
       if(resultList.size()==arr.length)
       {
           list.add(new ArrayList<>(resultList));
       }
       else
       {
           for(int i=0;i<arr.length;i++)
           {
               if(resultList.contains(arr[i]))
               {
                   continue;
               }
               resultList.add(arr[i]);
               permuteEvaluator(list, resultList, arr);
               resultList.remove(resultList.size()-1);
           }
       }
      
      
   }
   public static void main(String[] args)
   {
       PermutationofInt i=new PermutationofInt();
       int arr[]={1,5,4,2};
      
       List<List<Integer>> perm=i.gerPermute(arr);
       System.out.println("Permutations os array : [1,5,4,2] are :");
       System.out.println("************************************");
       for(List<Integer> p:perm)
       {
           System.out.println(p);
       }

   }

}