AdventOfCode/AdventOfCode.Solutions/2024/Day 04/Day04.cs

using AdventOfCode.Core.Shared.IO;
using System.Linq;
using System.Text.RegularExpressions;
using System.Threading.Tasks.Dataflow;

namespace AdventOfCode.Solutions._2024
{
    public class Day04 : IChallange
    {
        public int Year => 2024;

        public int Day => 4;

        private readonly IInputReader _inputReader;

        public Day04(IInputReader inputReader)
        {
            _inputReader = inputReader;
            _inputReader.SetInput(this);
        }

        //18
        //2514
        public async Task<string> GetSolutionPart1()
        {
            Grid<Point> grid = await _inputReader.ReadToGrid<Point>();
            int total = grid.FindWithValue('X').Sum(p => GetPossibleMatches(grid, p, "XMAS"));
            total += grid.FindWithValue('S').Sum(p => GetPossibleMatches(grid, p, "SAMX"));
            return total.ToString();
        }

        //9
        //1888 
        public async Task<string> GetSolutionPart2()
        {
            //_inputReader.SetSampleInput(true);
            Grid<Point> grid = await _inputReader.ReadToGrid<Point>();
            int total =  grid.FindWithValue('M').Where(p => IsValid(grid, p, 'S')).Count();
            total += grid.FindWithValue('S').Where(p => IsValid(grid, p, 'M')).Count();
            return total.ToString();
        }

        private static bool IsValid(Grid<Point> grid, Point p, char otherValue)
        {
            // validate the bounding box
            if (p.X + 3 > grid.Columns || p.Y + 3 > grid.Rows)
            {
                return false;
            }

            // check that +1,+1 from the point is A
            if (grid.GetNode(p.X + 1, p.Y + 1).Value != 'A')
            {
                return false;
            }

            if((grid.GetNode(p.X, p.Y).Value == 'M' && grid.GetNode(p.X + 2, p.Y + 2).Value == 'S' || grid.GetNode(p.X, p.Y).Value == 'S' && grid.GetNode(p.X + 2, p.Y + 2).Value == 'M')
                && (grid.GetNode(p.X, p.Y + 2).Value == 'M' && grid.GetNode(p.X + 2, p.Y).Value == 'S' || grid.GetNode(p.X, p.Y + 2).Value == 'S' && grid.GetNode(p.X + 2, p.Y).Value == 'M'))
                return true;

            return false;
        }

        private static int GetPossibleMatches(Grid<Point> grid, Point start, string word)
        {
            int matches = 0;

            bool canLookUp = start.Y + 1 >= word.Length,
                canLookForward = grid.Columns - start.X >= word.Length,
                canLookDown = grid.Rows - start.Y >= word.Length;

            // check up if possible
            if (canLookUp && canLookForward && IsMatch(grid, start, -1, 1, word))
            {
                matches++;
            }

            if (canLookForward && IsMatch(grid, start, 0, 1, word))
            {
                matches++;
            }

            if (canLookForward && canLookDown && IsMatch(grid, start, 1, 1, word))
            {
                matches++;
            }

            if (canLookDown && IsMatch(grid, start, 1, 0, word))
            {
                matches++;
            }

            return matches;
        }

        private static bool IsMatch(Grid<Point> grid,  Point start, int rowChange, int columnChange, string word)
        {
            for (int index = 1; index < word.Length; index++)
            {
                if (grid.GetNode(start.X + (columnChange * index), start.Y + (rowChange * index)).Value != word[index])
                    return false;
            }

            return true;
        }
    }
}