Advanced Recursion Techniques in C#

using System;
using System.Collections.Generic;

public class Permutations
{
    public static void Main(string[] args)
    {
        Permutations perm = new Permutations();
        List<List<int>> result = perm.Permute(new int[] { 1, 2, 3 });
        foreach (var list in result)
        {
            Console.WriteLine(string.Join(", ", list)); 
        }
        // Output: 
        // 1, 2, 3
        // 1, 3, 2
        // 2, 1, 3
        // 2, 3, 1
        // 3, 2, 1
        // 3, 1, 2
    }

    public List<List<int>> Permute(int[] nums)
    {
        List<List<int>> result = new List<List<int>>();
        Backtrack(nums, 0, result);
        return result;
    }

    private void Backtrack(int[] nums, int first, List<List<int>> result)
    {
        if (first == nums.Length)
        {
            List<int> current = new List<int>();
            foreach (int num in 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;
    }
}