AdventOfCode/Days/Day4.cs

using Spectre.Console;

namespace AdventOfCode.Days;

public class Day4 : Day
{
    public override int Number => 4;
    public override string Name => "Ceres Search";

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

        var grid = Input.AsCharGrid();

        for (int x = 0; x < grid.GetLength(0); x++)
        {
            for (int y = 0; y < grid.GetLength(1); y++)
            {
                xmasCount += CheckXmas(x, y);
            }
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Number of safe reports: [yellow]{xmasCount}[/][/]");
        }

        return;

        int CheckXmas(int x, int y)
        {
            (int xOffset, int yOffset)[] patterns = [
                (1, 0),
                (-1, 0),
                (0, 1),
                (0, -1),
                (1, 1),
                (1, -1),
                (-1, 1),
                (-1, -1)
            ];

            char[] word = ['X', 'M', 'A', 'S'];

            int count = 0;

            foreach (var pattern in patterns)
            {
                bool valid = true;

                for (int i = 0; i < word.Length; i++)
                {
                    var xTarget = x + (pattern.xOffset * i);
                    var yTarget = y + (pattern.yOffset * i);

                    if (xTarget < 0 || xTarget >= grid.GetLength(0)
                                    || yTarget < 0 || yTarget >= grid.GetLength(1)
                                    || word[i] != grid[xTarget, yTarget])
                    {
                        valid = false;

                        break;
                    }
                }

                if (valid)
                {
                    count++;
                }
            }

            return count;
        }
    }

    public override void RunPart2(bool display = true)
    {
        var xmasCount = 0;

        var grid = Input.AsCharGrid();

        for (int x = 0; x < grid.GetLength(0); x++)
        {
            for (int y = 0; y < grid.GetLength(1); y++)
            {
                xmasCount += CheckXmas(x, y);
            }
        }

        if (display)
        {
            AnsiConsole.MarkupLine($"[green]Number of safe reports: [yellow]{xmasCount}[/][/]");
        }

        return;

        int CheckXmas(int x, int y)
        {
            ((int xOffset, int yOffset) first, (int xOffset, int yOffset) second)[] patterns = [
                ((-1, -1), (-1, 1)),
                ((-1, -1), (1, -1)),
                ((1, -1), (1, 1)),
                ((1, 1), (-1, 1))
            ];

            char[] word = ['M', 'S'];

            // Center element of the cross must be an 'A'
            if (grid[x, y] != 'A')
            {
                return 0;
            }

            // Make sure we're not going out of bounds
            if (x - 1 < 0 || x + 1 >= grid.GetLength(0) ||
                y - 1 < 0 || y + 1 >= grid.GetLength(1))
            {
                return 0;
            }

            int count = 0;

            foreach (var (first, second) in patterns)
            {
                if (grid[x + first.xOffset, y + first.yOffset] is 'M' && grid[x - first.xOffset, y - first.yOffset] is 'S' &&
                    grid[x + second.xOffset, y + second.yOffset] is 'M' && grid[x - second.xOffset, y - second.yOffset] is 'S')
                {
                    count++;
                }
            }

            return count;
        }
    }
}