Task2

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

namespace ConsoleApp2
{
    public class CreateFileOrFolder
    {
        public static string GetRandomAlphaNumeric()
        {
            return Path.GetRandomFileName().Replace(".", "").Substring(0, 10);
        }

        static List<string> EveryNthElement(List<string> list, int nth)
        {
            IEnumerable<string> result = Enumerable.Empty<string>();
            result = list.Where((x, i) => i % nth != nth - 1);
            return result.ToList();
        }
        static void Main()
        {
            string folderName = @"c:\Task2\Proba4";

            string pathString = System.IO.Path.Combine(folderName, "Files");
            var directory = System.IO.Directory.CreateDirectory(pathString);

            string pathString1 = System.IO.Path.Combine(folderName, "files_generated.txt");
            var filesGenerated = System.IO.File.Create(pathString1);

            List<string> list = new List<string>();

            using (System.IO.StreamWriter file = new System.IO.StreamWriter(filesGenerated))
            {
                for (int i = 0; i < 11; i++)
                {
                    string fileName = GetRandomAlphaNumeric();
                    list.Add(fileName + ".txt");
                    file.WriteLine(fileName + ".txt");
                    var pathString2 = System.IO.Path.Combine(pathString, fileName + ".txt");
                    var newFile = System.IO.File.Create(pathString2);
                    newFile.Close();
                }
            }
            filesGenerated.Close();

            Console.WriteLine("files_generated.txt: ");
            Console.WriteLine(string.Join(",", list));
            list = list.OrderBy(a => a).ToList();

            string pathString3 = System.IO.Path.Combine(folderName, "files_sorted.txt");
            var filesSorted = System.IO.File.Create(pathString3);

            using (System.IO.StreamWriter file = new System.IO.StreamWriter(filesSorted))
            {
                for (int i = 0; i < list.Count; i++)
                {
                    file.WriteLine(list[i]);
                }
            }
            filesSorted.Close();

            Console.WriteLine("files_sorted.txt: ");
            Console.WriteLine(string.Join(",", list));

            string pathString4 = System.IO.Path.Combine(folderName, "files_deleted_1.txt");
            string pathString5 = System.IO.Path.Combine(folderName, "files_deleted_2.txt");

            var filesDeleted1List = EveryNthElement(list, 2);
            var filesDeleted2List = EveryNthElement(filesDeleted1List, 3);

            Console.WriteLine("files_deleted1.txt: ");
            Console.WriteLine(string.Join(",", filesDeleted1List));
            Console.WriteLine("files_deleted2.txt: ");
            Console.WriteLine(string.Join(",", filesDeleted2List));

            var filesDeleted1 = System.IO.File.Create(pathString4);
            using (System.IO.StreamWriter file = new System.IO.StreamWriter(filesDeleted1))
            {
                for (int i = 0; i < filesDeleted1List.Count; i++)
                {
                    file.WriteLine(filesDeleted1List[i]);
                }
            }
            filesDeleted1.Close();

            var filesDeleted2 = System.IO.File.Create(pathString5);

            using (System.IO.StreamWriter file2 = new System.IO.StreamWriter(filesDeleted2))
            {
                for (int i = 0; i < filesDeleted2List.Count; i++)
                {
                    file2.WriteLine(filesDeleted2List[i]);
                }
            }
            filesDeleted2.Close();

            Console.WriteLine("Files (files left total):  ");
            Console.WriteLine(string.Join(",", list));

            string pathStringDelete = System.IO.Path.Combine(folderName, "Files");

            list = filesDeleted2List;

            Console.WriteLine("FilesX (after delete files from Files that are not listed in the file_deleted_2.txt - so only files that are in file_deleted_2: ");
            Console.WriteLine(string.Join(",", list));

            System.IO.DirectoryInfo di = new DirectoryInfo(pathStringDelete);

            foreach (FileInfo file in di.GetFiles())
            {
                bool da = false;
                for (int i=0; i<list.Count; i++)
                {
                    if (file.Name == list[i].ToString()) da = true;
                }
                if (!da) file.Delete();
            }

            string pathStringX = System.IO.Path.Combine(folderName, "files_" + list.Count + ".txt");
            var filesX = System.IO.File.Create(pathStringX);

            using (System.IO.StreamWriter file = new System.IO.StreamWriter(filesX))
            {
                for (int i = 0; i < list.Count; i++)
                {
                    if (File.Exists(Path.Combine(pathStringDelete, list[i])))
                    {
                        file.WriteLine(list[i]);
                    }
                }
            }

            System.Console.WriteLine("Press any key to exit.");
            System.Console.ReadKey();
        }
    }
}