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 HashSet<Point2D>();
var tokens = parser.Parse(inputFile).ToList();
foreach (var token in tokens)
{
    if (token is SymbolToken sym)
    {
        foreach (var p in sym.Position.SurroundingAndSelf())
        {
            set.Add(p);
        }
    }
}

Console.WriteLine();

for (var y = 0; y < parser.Height; y++)
{
    for (var x = 0; x < parser.Width; x++)
    {
        if (set.Contains(new Point2D(x, y)))
        {
            Console.Write("X");
        }
        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}");

return 0;

int IsTouchingSymbol(ISet<Point2D> set, NumberToken num)
{
    for (var w = 0; w < num.Length; w++)
    {
        var p = num.Position with { X = num.Position.X + w };
        if (set.Contains(p))
        {
            return num.Value;
        }
    }

    return 0;
}