AdventOfCode23/Day3/Program.cs

using Day3;

if (args.Length < 1)
{
    Console.WriteLine("Requires 1 args: inputFileName");
    return -1;
}

var inputFile = args[0];
var parser = new SchematicParser();

var set = new Dictionary<Point2D, IList<Cell>>();
var cellList = new List<Cell>();
var tokens = parser.Parse(inputFile).ToList();
foreach (var token in tokens)
{
    if (token is SymbolToken sym)
    {
        var cell = new Cell(sym);
        cellList.Add(cell);
        foreach (var p in sym.Position.SurroundingAndSelf())
        {
            if (!set.ContainsKey(p))
            {
                set[p] = new List<Cell>();
            }
            
            set[p].Add(cell);
        }
    }
}

Console.WriteLine();

for (var y = 0; y < parser.Height; y++)
{
    for (var x = 0; x < parser.Width; x++)
    {
        var p = new Point2D(x, y);
        if (set.TryGetValue(p, out IList<Cell>? cells))
        {
            Console.Write(cells.Count);
        }
        else
        {
            Console.Write("-");
        }
    }
    Console.WriteLine("|");
}

var sum = 0;
foreach (var token in tokens)
{
    if (token is NumberToken num)
    {
        sum += IsTouchingSymbol(set, num);
    }
}

Console.WriteLine();
Console.WriteLine($"Sum: {sum}");

sum = cellList.Select(c => c.GearRatio()).Sum();
Console.WriteLine();
Console.WriteLine($"Gear ratio sum: {sum}");

return 0;

int IsTouchingSymbol(Dictionary<Point2D, IList<Cell>> set, NumberToken num)
{
    var touching = false;
    var cellMap = new HashSet<Cell>();
    for (var w = 0; w < num.Length; w++)
    {
        var p = num.Position with { X = num.Position.X + w };
        if (set.TryGetValue(p, out IList<Cell>? cells))
        {
            touching = true;
            foreach (var cell in cells)
            {
                if (!cellMap.Contains(cell))
                {
                    cell.Numbers.Add(num);
                    cellMap.Add(cell);
                }
            }
        }
    }

    return touching ? num.Value : 0;
}