AdventOfCode/AdventOfCode.Solutions/2023/Day 04/Day04.cs

using AdventOfCode.Core;

namespace AdventOfCode.Solutions._2023
{
    public class Day04(InputReader reader) : IChallange
    {
        private InputReader _inputReader = reader;

        private Dictionary<int, int> _cardRuns = new Dictionary<int, int> { { 1,  1 } };

        public async Task<string> GetSolutionPart1()
        {
            int total = 0;
            await foreach (string scratchCard in _inputReader.ReadAsStringLine())
            {
                int power = GetWinningMatches(scratchCard) - 1;
                if (power >= 0)
                {
                    total += (int)Math.Pow(2, power);
                }
            }

            return total.ToString();
        }

        public async Task<string> GetSolutionPart2()
        {
            int currentCard = 0;
            await foreach (string scratchCard in _inputReader.ReadAsStringLine())
            {
                currentCard++;
                _ = GetRuns(currentCard); // ensure that there is always atleast one run for the count
                for (int i = 1; i <= GetWinningMatches(scratchCard); i++) {
                    AddRunsToCard(currentCard + i, currentCard);
                }
            }

            return _cardRuns.Values.Sum().ToString();
        }

        private int GetWinningMatches(string card)
        {
            string[] numbers = card.Split(':')[1].Split('|');
            List<int> winners = numbers[0].Split(' ')
                .Where(s => !string.IsNullOrWhiteSpace(s))
                .Select(int.Parse)
                .ToList();

            return numbers[1].Split(' ')
                .Where(s => !string.IsNullOrWhiteSpace(s))
                .Select(int.Parse)
                .Where(winners.Contains)
                .Count();

        }

        private void AddRunsToCard(int card, int currentCard)
        {
            if (!_cardRuns.ContainsKey(card))
                _cardRuns.Add(card, 1);

            _cardRuns[card] += GetRuns(currentCard);
        }

        private int GetRuns(int card)
        {
            if (!_cardRuns.ContainsKey(card))
                _cardRuns.Add(card, 1);

            return _cardRuns[card];
        }
    }
}