simple C# concurrent word counter based on https://www.youtube.com/watch?v=B5xYBrxVSiE

wordcounter.cs

using System;
using System.IO;
using System.Linq;
using System.Diagnostics;
using System.Collections.Concurrent;

namespace wordcounter
{
    class Program
    {
        static void Main(string[] args)
        {
            var stopWatch = new Stopwatch();
            stopWatch.Start();
            
            // TODO: take command line parameter
            var textDirectory = @"C:\Users\Warren\Downloads\show-master\episode\9\text\";

            var finalTally = new ConcurrentDictionary<string, int>();

            Directory.GetFiles(textDirectory).AsParallel().ForAll((filePath) =>
            {
                var fileContents = File.ReadAllText(filePath);

                foreach (var word in fileContents.Split(null))
                {
                    var lowercased = word.ToLower();
                    finalTally.AddOrUpdate(lowercased, 1, (key, oldValue) => oldValue + 1);
                }
            });

            foreach (var entry in finalTally)
            {
                if (entry.Value > 1)
                {
                    Console.WriteLine(entry);
                }
            }

            stopWatch.Stop();

            Console.WriteLine(stopWatch.Elapsed);
            Console.ReadKey();
        }
    }
}