using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Linq;

​

[TestClass]

public class AA

{

    private static Random random = new Random();

        public static string RandomString(int length)

        {

            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

            return new string(Enumerable.Repeat(chars, length)

                .Select(s => s[random.Next(s.Length)]).ToArray());

        }

​

        [TestMethod]

        public void A()

        {

            int numberOfElements = 10 * 1000;

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

​

            for (int i = 0; i < numberOfElements; i++)

            {

                list.Add(RandomString(20));

            }

​

            HashSet<string> hash = new HashSet<string>(list);

            Dictionary<string, string> dictionary = list.ToDictionary(x => x, x => x);

​

            Stopwatch stopwatch = Stopwatch.StartNew();

​

​

            foreach (string s in list)

            {

                hash.TryGetValue(s, out string xx);

            }

​

            stopwatch.Stop();

            long hashTime = stopwatch.ElapsedMilliseconds;

​

            stopwatch.Restart();

​

            foreach (string s in list)

            {

                string singleOrDefault = list.SingleOrDefault(x => x == s);

            }

​

            stopwatch.Stop();

            long listTime = stopwatch.ElapsedMilliseconds;

​

            stopwatch.Restart();

​

            foreach (string s in list)

            {

                dictionary.TryGetValue(s, out string xx);

            }

​

            stopwatch.Stop();

            long dicTime = stopwatch.ElapsedMilliseconds;

​

            (hashTime + " " + dicTime + " " + listTime).Should().Be("");

        }

}