Question

Part III: Permutations (10 points) Write a recursive method public static ArrayList<int[] > permuteArray (int[] array) that returns an ArrayList of all permutations of the the parameter array. The ArrayList may contain the ar- rays in any order. Example: Suppose array = {4, 7, 1, 2}. Then the ArrayList would contain the following arrays, but in any order: 4 7 12 7 4 1 2 2 1 4 7 1 24 7 4 7 2 1 7 4 2 1 2 1 74 1 2 74 4 2 1 7 7 1 24 2 7 4 1 1 4 2 7 4 2 7 1 7 1 4 2 2 7 1 4 1 4 7 2 4 1 2 7 7 2 1 4 2 4 1 7 1 7 2 4 4.1 72 72 41 2 4 7 1 1 7 4 2 You are permitted to use at most two loops in solving this problem. A set of doubly-nested for-loops would count as two loops for this purpose. Recursion must be used in some non-trivial way to help solve the problem. You may write helper methods if you like.

in java

Answer 1

import java.util.ArrayList;

public class PermuteArray {
  
public static void main(String[]args)
{
int[] arr = {4, 7, 1, 2};
ArrayList<int[]> list = permuteArray(arr);
for(int i = 0; i < list.size(); i++)
{
if(i % 6 == 0 && i != 0)
System.out.println();
  
for(int j = 0; j < list.get(i).length; j++)
{
System.out.print(list.get(i)[j] + " ");
}
System.out.println();
}
}
  
public static ArrayList<int[]> permuteArray(int[] array)
{
ArrayList<int[]> result = new ArrayList<>();
helper(0, array, result);
return result;
}
  
private static void helper(int start, int[] nums, ArrayList<int[]> result)
{
if(start == nums.length - 1)
{
ArrayList<Integer> list = new ArrayList<>();
for(int num : nums)
{
list.add(num);
}
result.add(list.stream().mapToInt(Integer::intValue).toArray());
return;
}
for(int i = start; i < nums.length; i++)
{
swap(nums, i, start);
helper(start + 1, nums, result);
swap(nums, i, start);
}
}
  
private static void swap(int[] nums, int i, int j)
{
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
}

********************************************************************* SCREENSHOT ******************************************************

DD run: 4 7 1 2 4 7 2 1 4 1 7 2 4 1 2 7 4 2 1 7 4 2 7 1 7 4 1 2 7 4 2 1 7 1 4 2 7 1 2 4 7 2 1 4 7 2 4 1 1 74 2 1 7 2 4 1 47 2 1 4 27 1 2 4 7 1 27 4 2 7 1 4 2 7 4 1 2 17 4 2 1 47 2 4 1 7 2 4 7 1 BUILD SUCCESSFUL (total time: 0 seconds) A