Advanced Recursion Techniques in Java

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

public class Permutations {
    public static void main(String[] args) {
        Permutations perm = new Permutations();
        List<List<Integer>> result = perm.permute(new int[]{1, 2, 3});
        System.out.println(result); // Output: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 2, 1], [3, 1, 2]]
    }

    public List<List<Integer>> permute(int[] nums) {
        List<List<Integer>> result = new ArrayList<>();
        backtrack(nums, 0, result);
        return result;
    }

    private void backtrack(int[] nums, int first, List<List<Integer>> result) {
        if (first == nums.length) {
            List<Integer> current = new ArrayList<>();
            for (int num : nums) {
                current.add(num);
            }
            result.add(current);
        }
        for (int i = first; i < nums.length; i++) {
            swap(nums, first, i); // Swap numbers
            backtrack(nums, first + 1, result);
            swap(nums, first, i); // Swap them back to reset the state
        }
    }

    private void swap(int[] nums, int i, int j) {
        int temp = nums[i];
        nums[i] = nums[j];
        nums[j] = temp;
    }
}