AdventOfCode/Days/Day14.cs

using System.Collections.Frozen;
using System.Numerics;
using System.Text;
using Spectre.Console;

namespace AdventOfCode.Days;

public class Day14 : Day
{
    public override int Number => 14;
    public override string Name => "Restroom Redoubt";

    private const int Height = 103;
    private const int HeightCenter = Height / 2;

    private const int Width = 101;
    private const int WidthCenter = Width / 2;

    private const int Iterations = 100;

    public override void RunPart1(bool display = true)
    {
        var robots = ParseRobots();

        for (var i = 0; i < Iterations; i++)
        {
            foreach (var robot in robots)
            {
                robot.Position = new Point(
                    Math.Abs((Width + robot.Position.X + robot.Velocity.X) % Width),
                    Math.Abs((Height + robot.Position.Y + robot.Velocity.Y) % Height)
                );
            }
        }

        // Compute safety factor
        var safetyFactor =
            robots.Count(r => r.Position is { X: < WidthCenter, Y: < HeightCenter }) *
            robots.Count(r => r.Position is { X: > WidthCenter, Y: < HeightCenter }) *
            robots.Count(r => r.Position is { X: < WidthCenter, Y: > HeightCenter }) *
            robots.Count(r => r.Position is { X: > WidthCenter, Y: > HeightCenter });

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Safety factor: [yellow]{safetyFactor}[/][/]");
        }
    }

    public override void RunPart2(bool display = true)
    {
        var robots = ParseRobots();

        var canvas = new Canvas(Width, Height);

        for (var i = 0; i < int.MaxValue; i++)
        {
            for (var x = 0; x < Width; x++)
            {
                for (var y = 0; y < Height; y++)
                {
                    canvas.SetPixel(x, y, Color.Grey23);
                }
            }

            foreach (var robot in robots)
            {
                robot.Position = new Point(
                    Math.Abs((Width + robot.Position.X + robot.Velocity.X) % Width),
                    Math.Abs((Height + robot.Position.Y + robot.Velocity.Y) % Height)
                );

                canvas.SetPixel(robot.Position.X, robot.Position.Y, Color.Green1);
            }

            // Display grid
            if ((i + 1 - 46) % 101 == 0)
            {
                AnsiConsole.Write(canvas);
                AnsiConsole.WriteLine();

                AnsiConsole.Write($"Seconds elapsed: {i + 1}");

                var key = Console.ReadKey(true).Key;

                if (key is ConsoleKey.Enter)
                {
                    AnsiConsole.WriteLine();
                    AnsiConsole.WriteLine();
                    AnsiConsole.MarkupLine($"[green]Image at instant: [yellow]t={i + 1}s[/][/]");

                    break;
                }

                AnsiConsole.Clear();
            }
        }
    }

    private List<Robot> ParseRobots()
    {
        var robots = new List<Robot>();

        foreach (var line in Input.AsSpan().EnumerateLines())
        {
            var positionX = int.Parse(line[(line.IndexOf('=') + 1)..line.IndexOf(',')]);
            var positionY = int.Parse(line[(line.IndexOf(',') + 1)..line.IndexOf(' ')]);

            var velocityX = int.Parse(line[(line.LastIndexOf('=') + 1)..line.LastIndexOf(',')]);
            var velocityY = int.Parse(line[(line.LastIndexOf(',') + 1)..]);

            robots.Add(new Robot(new Point(positionX, positionY), new Point(velocityX, velocityY)));
        }

        return robots;
    }

    private class Robot(Point position, Point velocity)
    {
        public Point Position { get; set; } = position;
        public Point Velocity { get; } = velocity;
    }

    private readonly record struct Point(int X, int Y)
        : IAdditionOperators<Point, Point, Point>,
            ISubtractionOperators<Point, Point, Point>,
            IMultiplyOperators<Point, int, Point>
    {
        public static Point operator +(Point left, Point right)
        {
            return new Point(left.X + right.X, left.Y + right.Y);
        }

        public static Point operator -(Point left, Point right)
        {
            return new Point(left.X - right.X, left.Y - right.Y);
        }

        public static Point operator *(Point left, int right)
        {
            return new Point(left.X * right, left.Y * right);
        }

        public static Point operator *(int left, Point right)
        {
            return new Point(right.X * left, right.Y * left);
        }

        public static implicit operator Point((int X, int Y) point)
            => new(point.X, point.Y);
    }
}