path: root/Day14.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace aoc2019
{
    internal sealed class Day14 : Day
    {
        public override int DayNumber => 14;

        private Dictionary<string, long> available;
        private readonly Dictionary<string, Reaction> reactions;

        private struct Component
        {
            public string Name { get; set; }
            public int Quantity { get; set; }
        }

        private class Reaction
        {
            public readonly Component product;
            public readonly Component[] reactants;

            private Reaction(Component[] reactants, Component product)
            {
                this.reactants = reactants;
                this.product = product;
            }

            public static Reaction Parse(string s)
            {
                var ss = s.Split(new[] { ", ", " => " }, System.StringSplitOptions.None);

                return new Reaction(
                    ss.Take(ss.Length - 1).Select(ParseComponent).ToArray(),
                    ParseComponent(ss[^1])
                );

                static Component ParseComponent(string s)
                {
                    var spl = s.Split(' ', 2);
                    return new Component
                    {
                        Quantity = int.Parse(spl[0]),
                        Name = spl[1]
                    };
                }
            }
        }

        private bool Consume(string chem, long quantity)
        {
            if (quantity <= 0)
                throw new ArgumentOutOfRangeException();

            if (!available!.ContainsKey(chem))
                available[chem] = 0;

            if (available[chem] < quantity && !Produce(chem, quantity - available[chem]))
                return false;

            available[chem] -= quantity;
            return true;
        }

        private bool Produce(string chem, long quantity)
        {
            if (chem == "ORE")
                return false;

            var reaction = reactions[chem];
            var reactionCount = (long)Math.Ceiling((double)quantity / reaction.product.Quantity);

            foreach (var reactant in reaction.reactants)
                if (!Consume(reactant.Name, reactionCount * reactant.Quantity))
                    return false;

            available![chem] = available.GetValueOrDefault(chem) + reactionCount * reaction.product.Quantity;
            return true;
        }

        public Day14()
        {
            reactions = Input
                .Select(Reaction.Parse)
                .ToDictionary(r => r.product.Name);
        }

        public override string Part1()
        {
            available = new Dictionary<string, long> { { "ORE", long.MaxValue } };
            Consume("FUEL", 1);
            return $"{long.MaxValue - available["ORE"]}";
        }

        public override string Part2()
        {
            return "";
        }
    }
}