AdventOfCode23/Day18/Field.cs

namespace Day18;

public class Field
{
    private CellData[,]? _grid;
    private long _perimeter = 0L;

    public void Apply(List<Instruction> instructions)
    {
        var pos = new Vec(0, 0);
        var lines = new List<Line>();
        _perimeter = 0L;
        foreach (var inst in instructions)
        {
            var line = new Line(pos, Vec.Direction(inst.Dir), inst.Num);
            lines.Add(line);
            pos = pos.Add(line.Dir.Multiply(line.Length));
            _perimeter += line.Length;
        }

        var xNodes = lines.Select(l => l.Start.X).Order().Distinct().ToArray();
        var yNodes = lines.Select(l => l.Start.Y).Order().Distinct().ToArray();

        _grid = new CellData[xNodes.Length - 1, yNodes.Length - 1];
        for (var y = 0; y < yNodes.Length - 1; y++)
        {
            for (var x = 0; x < xNodes.Length - 1; x++)
            {
                var topLeft = new Vec(xNodes[x], yNodes[y]);
                var bottomRight = new Vec(xNodes[x + 1], yNodes[y + 1]);
                var cell = new CellData(topLeft, bottomRight);
                _grid[x, y] = cell;

                cell.Lines = lines
                    .Where(l => l.Dir.IsVertical && l.Start.X == topLeft.X)
                    .ToList();
                
                cell.Calculate();
            }
        }
    }

    public long GetArea()
    {
        if (_grid == null)
        {
            throw new NullReferenceException("_grid");
        }
        
        var count = 0L;
        for (var y = 0; y < _grid.GetLength(1); y++)
        {
            var crossings = 0;
            for (var x = 0; x < _grid.GetLength(0); x++)
            {
                var cell = _grid[x, y];
                crossings += cell.HasCrossing ? 1 : 0;
                if (crossings % 2 == 1)
                {
                    count += cell.Size();
                }
            }
        }

        count += _perimeter / 2 + 1;

        return count;
    }

    public void Print()
    {
        if (_grid == null)
        {
            throw new NullReferenceException("_grid");
        }
        
        for (var y = 0; y < _grid.GetLength(1); y++)
        {
            var crossings = 0;
            for (var x = 0; x < _grid.GetLength(0); x++)
            {
                var cell = _grid[x, y];
                crossings += cell.HasCrossing ? 1 : 0;
                if (crossings % 2 == 1)
                {
                    Console.Write('#');
                }
                else
                {
                    Console.Write('.');
                }
            }

            Console.WriteLine();
        }

        Console.WriteLine();
    }
}