使用LINQ生成排列

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        List<int> numbers = new List<int> { 1, 2, 3 };

        var permutations = numbers.Permutations();

        foreach (var permutation in permutations)
        {
            Console.WriteLine(string.Join(", ", permutation));
        }
    }
}

public static class Extensions
{
    public static IEnumerable<IEnumerable<T>> Permutations<T>(this IEnumerable<T> source)
    {
        if (source == null)
            throw new ArgumentNullException(nameof(source));

        return permutations(source.ToArray());
    }

    private static IEnumerable<IEnumerable<T>> permutations<T>(IEnumerable<T> source)
    {
        if (!source.Any())
            yield return Enumerable.Empty<T>();

        foreach (var element in source)
        {
            var remainingElements = source.Except(new[] { element });

            foreach (var permutation in permutations(remainingElements))
                yield return new[] { element }.Concat(permutation);
        }
    }
}