Adv2016/D16.1/Program.cs

using System;
using System.Collections;
using System.Text;

namespace D16._1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"Part 1 : {FillHardDrive(args[0], 272)}");
            Console.WriteLine($"Part 2 : {FillHardDrive(args[0], 35651584)}");
        }

        private static string FillHardDrive(string input, int diskSize)
        {
            bool[] bs = new bool[input.Length];
            for (int i = 0; i < input.Length; i++)
                bs[i] = input[i] == '1' ? true : false;

            var ba = new BitArray(bs);
            while (ba.Length < diskSize)
            {
                var bab = new BitArray(ba.Length * 2 + 1);
                var l = ba.Count;

                for (int i = 0; i < l; ++i)
                {
                    bab.Set(i, ba.Get(i));
                    bab.Set(l + l - i, !ba.Get(i));
                }

                ba = bab;
            }

            int le = diskSize;
            while (ba.Length > 17)
            {
                le /= 2;
                BitArray cs = new BitArray(le);
                for (int i = 0; i < le; ++i)
                {
                    var p = ((ba.Get(i * 2) ? 1 : 0) << 1) + (ba.Get(i * 2 + 1) ? 1 : 0);
                    cs.Set(i, p == 0b11 || p == 0b00);
                }
                ba = cs;
            }

            var sb = new StringBuilder();
            foreach (bool b in ba) sb.Append(b ? "1" : "0");
            return sb.ToString();
        }
    }
}