gistfile1.cs

class Program {
    static void Main(string[] args) {
        var dict = new ConcurrentDictionary<string, ConcurrentBag<string>>();
        Directory.GetFiles("/home/ormaaj/doc/text/ebooks/programming/unsorted")
                 .AsParallel()
                 .ForAll(x => dict.AddOrUpdate(
                      BitConverter.ToString(SHA256.Create().ComputeHash(File.OpenRead(x))),
                      new ConcurrentBag<string>() { x },
                      (y, z) => { z.Add(y); return z; }));
	}
}