Day17.cs

public class Day17
{
    public class ConwayCubes
    {
        public HashSet<(int x, int y, int z)> ActiveCubes;
        private HashSet<(int x, int y, int z)> ActiveCubesTmp;
        private readonly Dictionary<(int x, int y, int z), int> Neightbours;
        private static readonly List<(int x, int y, int z)> Offsets = new List<(int, int, int)>()
        {
            (1, 1,  0), (1, 0,  0), (1, -1,  0), (0, -1,  0), (-1, -1,  0), (-1, 0,  0), (-1, 1,  0), (0, 1,  0),
            (1, 1,  1), (1, 0,  1), (1, -1,  1), (0, -1,  1), (-1, -1,  1), (-1, 0,  1), (-1, 1,  1), (0, 1,  1), (0, 0,  1),
            (1, 1, -1), (1, 0, -1), (1, -1, -1), (0, -1, -1), (-1, -1, -1), (-1, 0, -1), (-1, 1, -1), (0, 1, -1), (0, 0, -1)
        };

        public ConwayCubes(string initialGrid)
        {
            ActiveCubes = new HashSet<(int, int, int)>();
            ActiveCubesTmp = new HashSet<(int, int, int)>();
            Neightbours = new Dictionary<(int, int, int), int>();
            // Parse Grid
            var rows = initialGrid.Split(Environment.NewLine);
            for (int x = 0; x < rows.Length; x++)
            {
                for (int y = 0; y < rows[x].Length; y++)
                {
                    if (rows[x][y] == '#')
                    {
                        ActiveCubes.Add((x, y, 0));
                    }
                }
            }
        }

        public int CalculateActiveCubesAfterNumCycles(int numCycles)
        {
            for (int i = 0; i < numCycles; i++)
            {
                ExecuteCycle();
            }

            return ActiveCubes.Count;
        }

        private void ExecuteCycle()
        {
            Neightbours.Clear();
            foreach (var cube in ActiveCubes)
            {
                TouchNeighbours(cube);
            }

            // Calculate new active grid
            ActiveCubesTmp.Clear();
            foreach (var (cube, count) in Neightbours)
            {
                if (count == 2 && ActiveCubes.Contains(cube))
                {
                    ActiveCubesTmp.Add(cube);
                } 
                else if (count == 3)
                {
                    ActiveCubesTmp.Add(cube);
                }
            }

            // Swap active sets
            var tmp = ActiveCubes;
            ActiveCubes = ActiveCubesTmp;
            ActiveCubesTmp = tmp;
        }

        private void TouchNeighbours((int x, int y, int z) cube)
        {
            foreach (var (x, y, z) in Offsets)
            {
                var pos = (cube.x + x, cube.y + y, cube.z + z);
                if (Neightbours.ContainsKey(pos))
                {
                    Neightbours[pos]++;
                } 
                else
                {
                    Neightbours[pos] = 1;
                }
            }
        }
    }

    public class ConwayCubesFourDimensional
    {
        public HashSet<(int x, int y, int z, int w)> ActiveCubes;
        private HashSet<(int x, int y, int z, int w)> ActiveCubesTmp;
        private readonly Dictionary<(int x, int y, int z, int w), int> Neightbours;
        private static readonly List<(int x, int y, int z, int w)> Offsets = new List<(int, int, int, int)>()
        {
            (1, 1, 0, 0), (1, 0, 0, 0), (1, -1, 0, 0), (0, -1, 0, 0), (-1, -1, 0, 0), (-1, 0, 0, 0), (-1, 1, 0, 0), (0, 1, 0, 0), (0, 0, 1, 0), (1, 1, 1, 0), (1, 0, 1, 0), (1, -1, 1, 0), (0, -1, 1, 0), (-1, -1, 1, 0), (-1, 0, 1, 0), (-1, 1, 1, 0), (0, 1, 1, 0), (0, 0, -1, 0), (1, 1, -1, 0), (1, 0, -1, 0), (1, -1, -1, 0), (0, -1, -1, 0), (-1, -1, -1, 0), (-1, 0, -1, 0), (-1, 1, -1, 0), (0, 1, -1, 0),
            (0, 0, 0, 1), (1, 1, 0, 1), (1, 0, 0, 1), (1, -1, 0, 1), (0, -1, 0, 1), (-1, -1, 0, 1), (-1, 0, 0, 1), (-1, 1, 0, 1), (0, 1, 0, 1), (0, 0, 1, 1), (1, 1, 1, 1), (1, 0, 1, 1), (1, -1, 1, 1), (0, -1, 1, 1), (-1, -1, 1, 1), (-1, 0, 1, 1), (-1, 1, 1, 1), (0, 1, 1, 1), (0, 0, -1, 1), (1, 1, -1, 1), (1, 0, -1, 1), (1, -1, -1, 1), (0, -1, -1, 1), (-1, -1, -1, 1), (-1, 0, -1, 1), (-1, 1, -1, 1),
            (0, 1, -1, 1), (0, 0, 0, -1), (1, 1, 0, -1), (1, 0, 0, -1), (1, -1, 0, -1), (0, -1, 0, -1), (-1, -1, 0, -1), (-1, 0, 0, -1), (-1, 1, 0, -1), (0, 1, 0, -1), (0, 0, 1, -1), (1, 1, 1, -1), (1, 0, 1, -1), (1, -1, 1, -1), (0, -1, 1, -1), (-1, -1, 1, -1), (-1, 0, 1, -1), (-1, 1, 1, -1), (0, 1, 1, -1), (0, 0, -1, -1), (1, 1, -1, -1), (1, 0, -1, -1), (1, -1, -1, -1), (0, -1, -1, -1), (-1, -1, -1, -1), (-1, 0, -1, -1), (-1, 1, -1, -1), (0, 1, -1, -1)
        };

        public ConwayCubesFourDimensional(string initialGrid)
        {
            ActiveCubes = new HashSet<(int, int, int, int)>();
            ActiveCubesTmp = new HashSet<(int, int, int, int)>();
            Neightbours = new Dictionary<(int, int, int, int), int>();
            // Parse Grid
            var rows = initialGrid.Split(Environment.NewLine);
            for (int x = 0; x < rows.Length; x++)
            {
                for (int y = 0; y < rows[x].Length; y++)
                {
                    if (rows[x][y] == '#')
                    {
                        ActiveCubes.Add((x, y, 0, 0));
                    }
                }
            }
        }

        public int CalculateActiveCubesAfterNumCycles(int numCycles)
        {
            for (int i = 0; i < numCycles; i++)
            {
                ExecuteCycle();
            }

            return ActiveCubes.Count;
        }

        private void ExecuteCycle()
        {
            Neightbours.Clear();
            foreach (var cube in ActiveCubes)
            {
                TouchNeighbours(cube);
            }

            // Calculate new active grid
            ActiveCubesTmp.Clear();
            foreach (var (cube, count) in Neightbours)
            {
                if (count == 2 && ActiveCubes.Contains(cube))
                {
                    ActiveCubesTmp.Add(cube);
                }
                else if (count == 3)
                {
                    ActiveCubesTmp.Add(cube);
                }
            }

            // Swap active sets
            var tmp = ActiveCubes;
            ActiveCubes = ActiveCubesTmp;
            ActiveCubesTmp = tmp;
        }

        private void TouchNeighbours((int x, int y, int z, int w) cube)
        {
            foreach (var (x, y, z, w) in Offsets)
            {
                var pos = (cube.x + x, cube.y + y, cube.z + z, cube.w + w);
                if (Neightbours.ContainsKey(pos))
                {
                    Neightbours[pos]++;
                }
                else
                {
                    Neightbours[pos] = 1;
                }
            }
        }
    }

    // == == == == == Puzzle 1 == == == == ==
    public static string Puzzle1(string input)
    {
        var cc = new ConwayCubes(input);
        return cc.CalculateActiveCubesAfterNumCycles(6).ToString();
    }

    // == == == == == Puzzle 2 == == == == ==
    public static string Puzzle2(string input)
    {
        var cc4d = new ConwayCubesFourDimensional(input);
        return cc4d.CalculateActiveCubesAfterNumCycles(6).ToString();
    }
}