using System;

using System.Diagnostics;

using System.Collections.Generic;

using System.Linq;

​

namespace test 

{

    public class Test

    {

        public static string[] BuildStringSequence(Random rnd, int size)

        {

            var result = new string[size];

            var matchingsPercent = size * 10;

            for (var i = 0; i < size; i++)

            {

                result[i] = rnd.Next(matchingsPercent).ToString();

            }

            return result;

        }

​

        public static void Main(string[] args)

        {

            var first = BuildStringSequence(new Random(1), 7000);

            var second = BuildStringSequence(new Random(2), 7000);

​

            var stopWatch = new Stopwatch();

            stopWatch.Start();

            var matchings = AlgorithmToImprove(first, second);

            stopWatch.Stop();

            var ts = stopWatch.Elapsed;

            Console.WriteLine(matchings.Length);

            Console.WriteLine(ts.TotalMilliseconds);

        }

​

        private static string[] AlgorithmToImprove(IEnumerable<string> first, IEnumerable<string> second)

        {

            return first.Where(x => second.Any(y => y == x)).Distinct().ToArray();

        }

    }

}