AdventOfCode23/Day7/Hand.cs

namespace Day7;

public class Hand : IComparable<Hand>
{
    private static readonly Dictionary<Predicate<int[]>, int> Types = new Dictionary<Predicate<int[]>, int>
    {
        [counts => counts[0] == 5] = 7,
        [counts => counts[0] == 4] = 6,
        [counts => counts[0] == 3 && counts[1] == 2] = 5,
        [counts => counts[0] == 3] = 4,
        [counts => counts[0] == 2 && counts[1] == 2] = 3,
        [counts => counts[0] == 2] = 2,
        [_ => true] = 1,
    };

    private static readonly string CardOrder = "23456789TJQKA";
    
    public string Cards { get; }
    public int Type { get; }
    public int Bid { get; }

    public Hand(string cards, int bid)
    {
        Cards = cards;
        Bid = bid;
        Type = GetHandType();
    }

    private int GetHandType()
    {
        var set = new Dictionary<char, int>();
        foreach (var c in Cards)
        {
            set.TryAdd(c, 0);
            set[c]++;
        }

        var counts = set.Values.OrderDescending().ToArray();

        return Types.First(kvp => kvp.Key(counts)).Value;
    }

    public int CompareTo(Hand? other)
    {
        // this < other => negative
        var typeCmp = Type.CompareTo(other?.Type);
        if (typeCmp != 0)
            return typeCmp;
        
        for (var i = 0; i < Cards.Length; i++)
        {
            var cardCmp = CompareCard(Cards[i], other!.Cards[i]);
            if (cardCmp != 0)
            {
                return cardCmp;
            }
        }

        throw new Exception("Not expecting equal hands");
    }

    private int CompareCard(char left, char right)
    {
        var vLeft = CardOrder.IndexOf(left);
        var vRight = CardOrder.IndexOf(right);

        return vLeft.CompareTo(vRight);
    }
}