AdventOfCode/2022/Day20CSharp/Advent2022_Day20.cs

// See https://aka.ms/new-console-template for more information

using System.Numerics;

var exampleData = new ProblemData("example-input.txt");
Console.WriteLine("Grove Coordinates, Example: " + exampleData.GetGroveCoordinates(1,1));

var puzzleData = new ProblemData("puzzle-input.txt");
Console.WriteLine("Grove Coordinates, Puzzle: " + puzzleData.GetGroveCoordinates(1,1));

Console.WriteLine("Grove Coordinates, Example Decrypted: " + exampleData.GetGroveCoordinates(811589153, 10));
Console.WriteLine("Grove Coordinates, Puzzle Decrypted: " + puzzleData.GetGroveCoordinates(811589153, 10));


class Item
{
    public Item(BigInteger value)
    {
        Value = value;
    }

    public BigInteger Value { get; set; }

    public override string ToString()
    {
        return Value.ToString();
    }
}

class CircularList
{
    public List<Item> Items;

    public CircularList()
    {
        Items = new List<Item>();
    }

    public void Add(Item item)
    {
        Items.Add(item);
    }

    public void Move(int oldIndex, int newIndex)
    {
        if (oldIndex == newIndex) return;

        var temp = Items[oldIndex];

        if (newIndex == 0)
        {
            Items.RemoveAt(oldIndex);
            Items.Add(temp);
        }
        else if (newIndex == Items.Count - 1)
        {
            Items.RemoveAt(oldIndex);
            Items.Insert(0, temp);
        }
        else
        {
            Items.RemoveAt(oldIndex);
            Items.Insert(newIndex, temp);
        }
    }

    public static void PrintList(CircularList list)
    {
        for (int ci = 0; ci < list.Items.Count; ci++)
        {
            if (ci != 0) Console.Write(", ");
            Console.Write(list.Items[ci]);
        }
        Console.WriteLine();
    }

    public static CircularList GetMixedList(CircularList source, BigInteger decryptionKey, int mixes)
    {
        var newList = new CircularList();

        for (int i = 0; i < source.Items.Count; i++)
        {
            source.Items[i].Value *= decryptionKey;

            newList.Items.Add(source.Items[i]);
        }

        for (int mixNum = 0; mixNum < mixes; mixNum++)
        {
            if (DebugPrint) Console.WriteLine("Starting mix {0} of {1}", mixNum + 1, mixes);
            
            for (int i = 0; i < source.Items.Count; i++)
            {
                if (DebugPrint) Console.WriteLine("|- Mixing item {0} of {1}", i + 1, source.Items.Count);

                var item = source.Items[i];

                int currentIndex = newList.Items.IndexOf(item);
                int direction = item.Value > 0 ? 1 : -1;
                int newIndex = currentIndex;

                BigInteger max = BigInteger.Abs(item.Value) % (source.Items.Count-1);

                for (BigInteger j = 0; j < max; j++)
                {
                    if (direction == 1 && newIndex == source.Items.Count - 1) newIndex = 1;
                    else if (direction == -1 && newIndex == 0) newIndex = source.Items.Count - 2;
                    else newIndex += direction;
                }

                newList.Move(currentIndex, newIndex);
            }
        }

        return newList;
    }

    public static bool DebugPrint { get; set; } = false;
}

class ProblemData
{
    private CircularList Numbers { get; set; }

    public CircularList GetMixedList(BigInteger decryptionKey, int mixes)
    {

        return CircularList.GetMixedList(Numbers, decryptionKey, mixes);
    }

    public BigInteger GetGroveCoordinates(BigInteger decryptionKey, int mixes)
    {
        BigInteger sum = 0;

        var list = GetMixedList(decryptionKey, mixes);

        int index = list.Items.FindIndex(x => x.Value == 0);

        for (int i = 0; i <= 3000; i++)
        {
            if (i % 1000 == 0)
            {
                sum += list.Items[index].Value;
            }

            if (index == list.Items.Count-1)
            {
                index = 0;
            }
            else
            {
                index++;
            }
        }

        return sum;
    }

    public ProblemData(string filename)
    {
        Numbers = new CircularList();

        using (StreamReader reader = System.IO.File.OpenText(filename))
        {
            while (!reader.EndOfStream)
            {
                var line = reader.ReadLine();
                if (line == null) throw new InvalidDataException();

                var value = Int32.Parse(line);

                Numbers.Add(new Item(value));
            }
        }
    }
}