AdventOfCode/Days/Day15.cs

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

namespace AdventOfCode.Days;

public class Day15 : Day
{
    public override int Number => 15;
    public override string Name => "Warehouse Woes";

    private const int Size = 50;

    private const char Wall = '#';
    private const char Box = 'O';
    private const char Empty = '.';

    private const char InstructionLeft = '<';
    private const char InstructionRight = '>';
    private const char InstructionUp = '^';
    private const char InstructionDown = 'v';

    public override void RunPart1(bool display = true)
    {
        var (map, position, instructions) = ParseMap();

        foreach (var instruction in instructions)
        {
            var direction = instruction switch
            {
                InstructionLeft => new Point(-1, 0),
                InstructionRight => new Point(1, 0),
                InstructionUp => new Point(0, -1),
                InstructionDown => new Point(0, 1),
                _ => throw new ArgumentException($"Invalid instruction: {instruction}")
            };

            var destination = position + direction;

            // Destination is free, just move
            if (map[destination.X, destination.Y] is not (Wall or Box))
            {
                position = destination;
            }
            // Destination is a box, check if there is a free space further up and move accordingly
            else if (map[destination.X, destination.Y] is Box)
            {
                var pushTarget = destination + direction;

                while (map[pushTarget.X, pushTarget.Y] is Box)
                {
                    pushTarget += direction;
                }

                // Cannot move anything since there is a wall
                if (map[pushTarget.X, pushTarget.Y] is Wall)
                {
                    continue;
                }

                // Move robot and boxes (only need to move first and last box of a chain)
                position = destination;

                map[destination.X, destination.Y] = Empty;
                map[pushTarget.X, pushTarget.Y] = Box;
            }
            // Else destination is a wall, do nothing
        }

        var coordinatesSum = 0;

        // Count gps coordinates
        for (var x = 0; x < Size; x++)
        {
            for (var y = 0; y < Size; y++)
            {
                if (map[x, y] is Box)
                {
                    coordinatesSum += 100 * y + x;

                }
            }
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Sum of boxes GPS coordinates: [yellow]{coordinatesSum}[/][/]");
        }
    }

    private static void DisplayGrid(char[,] map)
    {
        for (var y = 0; y < Size; y++)
        {
            for (var x = 0; x < Size; x++)
            {
                AnsiConsole.Write(map[x, y]);
            }

            AnsiConsole.WriteLine();
        }

        AnsiConsole.WriteLine();
    }

    public override void RunPart2(bool display = true)
    {

    }

    private (char[,] Map, Point Start, List<char> Instructions) ParseMap()
    {
        var readingMap = true;

        var map = new char[Size, Size];

        Point start = default;

        var instructions = new List<char>();

        var y = 0;
        foreach (var line in Input.AsSpan().EnumerateLines())
        {
            if (line.IsWhiteSpace())
            {
                readingMap = false;

                continue;
            }

            if (readingMap)
            {
                var x = 0;
                foreach (var symbol in line)
                {
                    map[x, y] = Empty;

                    if (symbol is Wall or Box)
                    {
                        map[x, y] = symbol;
                    }
                    else if (symbol is '@')
                    {
                        start = new Point(x, y);
                    }

                    x++;
                }

                y++;
            }
            else
            {
                foreach (var instruction in line)
                {
                    instructions.Add(instruction);
                }
            }
        }

        return (map, start, instructions);
    }

    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);
    }
}