using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Security.Cryptography;
private static byte[] LE64Count(IReadOnlyList<byte[]> pieces) => BitConverter.GetBytes((long)pieces.Count).Concat(pieces.SelectMany(piece => BitConverter.GetBytes((long)piece.Length).Concat(piece))).ToArray();
public static void Main(string[] args)
List<byte[]> pieces = new List<byte[]>
Encoding.UTF8.GetBytes("Hello"),
Encoding.UTF8.GetBytes("World"),
Encoding.UTF8.GetBytes("123"),
byte[] result = LE64Count(pieces);
Console.WriteLine(BitConverter.ToString(result));