AdventOfCode23/Day10/Grid.cs

using System.Text;

namespace Day10;

public class Grid
{
    private readonly int _width;
    private readonly int _height;
    private Tile? _start;
    public Tile?[,] Tiles { get; }

    public Grid(Tile?[,] tiles, int width, int height)
    {
        _width = width;
        _height = height;
        Tiles = tiles;
    }

    public void Print()
    {
        for (var y = 0; y < _height; y++)
        {
            var lineBuilder = new StringBuilder();
            for (var x = 0; x < _width; x++)
            {
                lineBuilder.Append(Tiles[x, y]?.Display ?? " ");
            }
            Console.WriteLine(lineBuilder);
        }
    }

    public int Follow()
    {
        foreach (var t in Tiles)
        {
            if (t?.Pipe == 'S')
            {
                _start = t;
                break;
            }
        }
        if (_start == null)
        {
            throw new Exception("Start is not set yet");
        }
        var queue = new Queue<(Tile Tile, GridPoint Source, int Index)>();
        var num = 0;
        queue.Enqueue((_start, _start.Position, 0));

        while (queue.Count > 0)
        {
            var (tile, source, index) = queue.Dequeue();
            
            if (tile.HasDisplay)
            {
                return index;
            }
            
            foreach (var next in tile.GetConnections()
                         .Where(n => n != source)
                         .Select(x => this[x])
                         .Where(t => t?.ConnectsTo(tile.Position) ?? false))
            {
                queue.Enqueue((next!, tile.Position, index + 1));
            }
            
            tile.SetDisplay(index);

            num++;
            if (num % 100 == 0)
            {
                Print();
                Console.WriteLine();
            }
        }

        throw new Exception("No cycle found");
    }

    public Tile? this[GridPoint point]
    {
        get
        {
            if (point.X < 0 || point.Y < 0 || point.X >= _width || point.Y >= _height)
            {
                return null;
            }

            return Tiles[point.X, point.Y];
        }
    }
}