Day4.cs

using System.Diagnostics;

namespace Implementation;

public class Day4
{
    public static int Part1(string input)
    {
        var lines = input.Split('\n').Where(x => x is not null).ToArray();
        var drawOrder = lines[0].Split(',').Select(int.Parse).ToArray();

        var boards = lines.Skip(1).Select((x, i) => (x, i)).GroupBy(x => x.i / 6).Where(x => x.Count() != 1).Select(g =>
        {
            Debug.Assert(g.First().x == string.Empty);
            Debug.Assert(g.Count() == 6);

            return g.Skip(1).Take(5).Select(x => x.x).Select(x => x.Split(' ').Where(x => !string.IsNullOrWhiteSpace(x)).Select(int.Parse).Select(x => new int?(x)).ToArray())
                .ToArray();
        }).ToArray();

        foreach (var drawn in drawOrder)
        {
            for (int b = 0; b < boards.Length; b++)
            {
                ref var board = ref boards[b];
                for (int i = 0; i < board.Length; i++)
                {
                    ref var row = ref board[i];
                    for (int j = 0; j < row.Length; j++)
                    {
                        if (row[j] == drawn)
                        {
                            row[j] = null;
                        }
                    }
                }
            }

            var done = boards.Where(x =>
            {
                // check if a board is done in here
                if (x.Any(x2 => x2.All(x3 => !x3.HasValue)))
                    return true;
                if (Enumerable.Range(0, x[0].Length).Any(i => x.Select(x2 => x2[i]).All(x3 => !x3.HasValue)))
                    return true;

                // if (Enumerable.Range(0, x[0].Length).All(i => !x[i][i].HasValue))
                //     return true;
                // 
                // if (Enumerable.Range(0, x[0].Length).All(i => !x[i][x[i].Length - i - 1].HasValue))
                //     return true;

                return false;
            });

            bool anyDone = false;
            int maxScore = 0;
            foreach (var v in done)
            {
                Console.WriteLine($"Found done board after drawing {drawn}");
                anyDone = true;
                maxScore = Math.Max(maxScore, v.SelectMany(x => x).Where(x => x.HasValue).Sum(x => x.Value) * drawn);
            }

            if (anyDone)
                return maxScore;
        }

        throw null;
    }
    public static int Part2(string input)
    {
        var lines = input.Split('\n').Where(x => x is not null).ToArray();
        var drawOrder = lines[0].Split(',').Select(int.Parse).ToArray();

        int finalScore = 0;
        var boards = lines.Skip(1).Select((x, i) => (x, i)).GroupBy(x => x.i / 6).Where(x => x.Count() != 1).Select(g =>
        {
            Debug.Assert(g.First().x == string.Empty);
            Debug.Assert(g.Count() == 6);

            return g.Skip(1).Take(5).Select(x => x.x).Select(x => x.Split(' ').Where(x => !string.IsNullOrWhiteSpace(x)).Select(int.Parse).Select(x => new int?(x)).ToArray())
                .ToArray();
        }).ToArray();

        foreach (var drawn in drawOrder)
        {
            for (int b = 0; b < boards.Length; b++)
            {
                ref var board = ref boards[b];
                for (int i = 0; i < board.Length; i++)
                {
                    ref var row = ref board[i];
                    for (int j = 0; j < row.Length; j++)
                    {
                        if (row[j] == drawn)
                        {
                            row[j] = null;
                        }
                    }
                }
            }

            var done = boards.Where(x =>
            {
                // check if a board is done in here
                if (x.Any(x2 => x2.All(x3 => !x3.HasValue)))
                    return true;
                if (Enumerable.Range(0, x[0].Length).Any(i => x.Select(x2 => x2[i]).All(x3 => !x3.HasValue)))
                    return true;

                // if (Enumerable.Range(0, x[0].Length).All(i => !x[i][i].HasValue))
                //     return true;
                // 
                // if (Enumerable.Range(0, x[0].Length).All(i => !x[i][x[i].Length - i - 1].HasValue))
                //     return true;

                return false;
            }).ToArray();

            foreach (var v in done)
            {
                finalScore = v.SelectMany(x => x).Where(x => x.HasValue).Sum(x => x.Value) * drawn;
            }

            boards = boards.Where(x => !done.Contains(x)).ToArray();
        }

        return finalScore;
    }
}