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

namespace ABC
{
    static class Program
    {
        static void Main(string[] args)
        {
            List<int> L = new List<int>() { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, };

            List<int> L2 = L.Swap(0, 9).ShowConsole().ToList();

            return;
        }

        public static IEnumerable<T> Swap<T>(this IEnumerable<T> Collection, int IdxA, int IdxB)
        {
            for (int i = 0; i < Collection.Count(); i++)
            {
                if (i == IdxA)
                {
                    yield return Collection.ElementAt(IdxB);
                    continue;
                }
                if (i == IdxB)
                {
                    yield return Collection.ElementAt(IdxA);
                    continue;
                }
                yield return Collection.ElementAt(i);
            }
        } 
        public static IEnumerable<T> ShowConsole<T>(this IEnumerable<T> Collection)
        {

            foreach (var o in Collection)
            {
                Console.WriteLine(o);
            }

            return Collection;
        }
    }
}