ДЗ: Объединение в одну коллекцию

.cs

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

namespace ConsoleApp1
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.InputEncoding = Encoding.Unicode;
            Console.OutputEncoding = Encoding.Unicode;

            List<int> list1 = new List<int>() { 1, 2, 1 };
            List<int> list2 = new List<int>() { 3, 2 };

            PrintList(list1, "Список 1: ");
            PrintList(list2, "Список 2: ");

            List<int> result = MergetLists(list1, list2);

            PrintList(result, "Результат: ");
        }

        static List<int> MergetLists(List<int> list1, List<int> list2)
        {
            List<int> mergedList = new List<int>();

            AddToList(list1, ref mergedList);
            AddToList(list2, ref mergedList);

            return mergedList;
        }

        static void AddToList(List<int> startList, ref List<int> resultList)
        {
            foreach (int item in startList)
            {
                if (resultList.Contains(item) == false)
                {
                    resultList.Add(item);
                }
            }
        }

        static void PrintList(List<int> list, string listName)
        {
            Console.WriteLine(listName);
            string joinedText = string.Empty;

            foreach (int number in list)
            {
                joinedText += number.ToString() + " ";
            }

            Console.WriteLine(joinedText);
        }
    }
}