Files

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace GerryTutor
{
    class Program
    {

        static List<double> Union(List<double> a, List<double> b)
        {
            List<double> result = new List<double>();
            foreach (var item in a)
            {
                if (!result.Contains(item))
                {
                    result.Add(item);
                }
            }
            foreach (var item in b)
            {
                if (!result.Contains(item))
                {
                    result.Add(item);
                }
            }
            return result;
        }
        static List<int> NonRepeat(int[] arr)
        {
            HashSet<int> set = new HashSet<int>();
            foreach (var item in arr)
            {
                set.Add(item);
            }
            return set.ToList();
        }
        static void Main(string[] args)
        {
            /* Ex 8
             * string filename = Console.ReadLine();
            if (File.Exists(filename))
            {
                using (StreamReader reader = new StreamReader(filename))
                {
                    string line;
                    int cnt = 0;
                    while ((line = reader.ReadLine()) != null)
                    {
                        cnt++;
                    }
                    Console.WriteLine($"Lines count: {cnt}");
                }
            }
            else
            {
                Console.WriteLine("File not found!");
            }*/
            HashSet<string> namesset = new HashSet<string>();
            using (StreamReader reader = new StreamReader("rats.txt"))
            {
                string line;
                while ((line = reader.ReadLine()) != null)
                {
                    namesset.Add(line);
                }
            }

            using (StreamWriter writer = new StreamWriter("out.txt"))
            {
                foreach (var item in namesset)
                {
                    writer.WriteLine(item);
                }
                Console.WriteLine("Writed....");
            }

        }
    }
}