using System;

using System.Linq;

using System.Diagnostics;

using System.Collections.Generic;

​

public class Program

{

    private static void Benchmark(Action act, int iterations)

    {

        GC.Collect();

        act.Invoke(); // run once outside of loop to avoid initialization costs

        Stopwatch sw = Stopwatch.StartNew();

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

        {

            act.Invoke();

        }

        sw.Stop();

        Console.WriteLine((sw.ElapsedTicks).ToString());

    }

​

    public static void Main(string[] args)

    {

        var x = Enumerable.Range(0, 1000).ToList();

        var y = Enumerable.Range(500, 1000).ToList();

        var a = Enumerable.Range(0, 10).ToList();

        var b = Enumerable.Range(5, 10).ToList();

        ICollection<int> g = x;

        ICollection<int> h = b;

        Benchmark(() => { x.Concat(y).Distinct().ToList(); }, 100);

        Benchmark(() => { x.Union(y).ToList(); }, 100);

        Benchmark(() => {  foreach (var i in y.Except(g)) g.Add(i); }, 100);

        Benchmark(() => { b.Concat(a).Distinct().ToList(); }, 100);

        Benchmark(() => { b.Union(a).ToList(); }, 100);

        Benchmark(() => { foreach (var i in a.Except(h)) h.Add(i); }, 100);

    }

}