using System;

using System.Collections.Generic;

using System.Linq;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {

        var keyNoAfs = Enumerable.Range(1, 13000).ToArray();

        var invalidWorkflows = Enumerable.Range(6000, 50000).Select(e => new { Status = "Invalid Status", KEY_NO_AF = e }).ToList();

        var sw = Stopwatch.StartNew();

        var validWorkflows = keyNoAfs.Except(invalidWorkflows.Select(i => i.KEY_NO_AF)).ToList();

        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        var invalidDictionary = invalidWorkflows.GroupBy(i => i.KEY_NO_AF).Select(i => i.First()).ToDictionary(i => i.KEY_NO_AF);

        var validWorkflows2 = keyNoAfs.Where(k => !invalidDictionary.ContainsKey(k)).ToList();

        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

        var invalidWorkflowList = invalidWorkflows.Select(X => X.KEY_NO_AF).ToList();             

        var validWorkflows3 = keyNoAfs.Where(Y => !invalidWorkflowList.Contains(Y)).ToList(); 

        sw.Stop();

        Console.WriteLine(sw.ElapsedMilliseconds);

        sw.Restart();

    }

}