UnionCollections

using System;
using System.Collections.Generic;

namespace CSLight
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] firstArray = InputStringArray(' ');
            string[] secondArray = InputStringArray(' ');
            List<string> result = UnionArrays(firstArray, secondArray);
            Console.WriteLine("Итоговая коллекция: ");
            PrintCollection(result);
        }

        private static void PrintCollection<T>(IList<T> collection)
        {
            foreach (T element in collection)
            {
                Console.Write($"{element} ");
            }
            Console.WriteLine();
        }

        private static List<T> UnionArrays<T>(IList<T> firstCollection, IList<T> secondCollection)
        {
            List<T> unionCollection = new List<T>(firstCollection);
            unionCollection.AddRange(secondCollection);
            return Distinct(unionCollection);
        }

        private static List<T> Distinct<T>(IList<T> collection)
        {
            List<T> distinctCollection = new List<T>();
            foreach (T element in collection)
            {
                if(distinctCollection.Contains(element) == false)
                    distinctCollection.Add(element);
            }

            return distinctCollection;
        }

        private static string[] InputStringArray(char separator)
        {
            Console.WriteLine($"Введите массив через '{separator}'");
            string text = Console.ReadLine();
            string[] result = text.Split(separator);
            return result;
        }
    }
}