AdventOfCode/Days/Day10.cs

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

namespace AdventOfCode.Days;

public class Day10 : Day
{
    public override int Number => 10;
    public override string Name => "Hoof It";

    private const int MapSize = 60;

    public override void RunPart1(bool display = true)
    {
        var hikingTrailsScores = 0;

        var (heightMap, trailHeads) = ParseMap();

        var hikingTrails = new HashSet<Point>();

        foreach (var trailHead in trailHeads)
        {
            hikingTrails.Clear();

            GetHikingTrailScore(trailHead, -1);

            hikingTrailsScores += hikingTrails.Count;
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Sum of scores of hiking trails: [yellow]{hikingTrailsScores}[/][/]");
        }

        return;

        void GetHikingTrailScore(Point position, int previousHeight)
        {
            // Out of bounds
            if (position is { X: < 0 or >= MapSize } or { Y: < 0 or >= MapSize })
            {
                return;
            }

            var height = heightMap[position.X, position.Y];

            if (height - previousHeight is not 1)
            {
                return;
            }

            if (height == 9)
            {
                hikingTrails.Add(position);
            }


            GetHikingTrailScore(position + (1, 0), height);
            GetHikingTrailScore(position + (-1, 0), height);
            GetHikingTrailScore(position + (0, 1), height);
            GetHikingTrailScore(position + (0, -1), height);
        }
    }

    public override void RunPart2(bool display = true)
    {
        var (heightMap, trailHeads) = ParseMap();

        var totalRating = 0;

        foreach (var trailHead in trailHeads)
        {
            GetHikingTrailRating(trailHead, -1);
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Total rating of hiking trails: [yellow]{totalRating}[/][/]");
        }

        return;

        void GetHikingTrailRating(Point position, int previousHeight)
        {
            // Out of bounds
            if (position is { X: < 0 or >= MapSize } or { Y: < 0 or >= MapSize })
            {
                return;
            }

            var height = heightMap[position.X, position.Y];

            if (height - previousHeight is not 1)
            {
                return;
            }

            if (height == 9)
            {
                totalRating++;
            }

            GetHikingTrailRating(position + (1, 0), height);
            GetHikingTrailRating(position + (-1, 0), height);
            GetHikingTrailRating(position + (0, 1), height);
            GetHikingTrailRating(position + (0, -1), height);
        }
    }

    private (byte[,] HeightMap, List<Point> TrailHeads) ParseMap()
    {
        var heightMap = new byte[MapSize, MapSize];
        var trailHeads = new List<Point>();

        var y = 0;
        foreach (var line in Input.AsSpan().EnumerateLines())
        {
            var x = 0;
            foreach (var height in line)
            {
                var heightValue = height - '0';

                if (heightValue is 0)
                {
                    trailHeads.Add(new Point(x, y));
                }

                heightMap[x, y] = (byte)heightValue;

                x++;
            }

            y++;
        }

        return (heightMap, trailHeads);
    }


    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);
    }
}