Day 14 - Part 1

Day14/Day14.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+namespace Advent
+{
+    public static class Day14
+    {
+        private class Reagent
+        {
+            public string Name { get; }
+            public int Count { get; }
+
+            public Reagent(string s)
+            {
+                var parts = s.Split(' ');
+
+                Name = parts[1];
+                Count = int.Parse(parts[0]);
+            }
+        }
+
+        private class Reaction
+        {
+            public Reagent Result { get; }
+            public List<Reagent> Components { get; } = new List<Reagent>();
+
+            public Reaction(string s)
+            {
+                var reactionParts = s.Split("=>").Select(s2 => s2.Trim()).ToArray();
+
+                Result = new Reagent(reactionParts[1]);
+
+                var reagentParts = reactionParts[0].Split(',').Select(s2 => s2.Trim()).ToArray();
+
+                foreach (var reagentPart in reagentParts)
+                {
+                    Components.Add(new Reagent(reagentPart));
+                }
+            }
+        }
+
+        private static readonly Dictionary<string, Reaction> Reactions = new Dictionary<string, Reaction>();
+        private static readonly Dictionary<string, int> Inventory = new Dictionary<string, int>();
+
+        public static void Execute()
+        {
+            var lines = File.ReadAllLines(@".\Day14\input.txt");
+
+            foreach (var line in lines)
+            {
+                var reaction = new Reaction(line);
+
+                Reactions[reaction.Result.Name] = reaction;
+
+                Inventory[reaction.Result.Name] = 0;
+            }
+
+            var oreRequired = GetRequiredOre("FUEL", 1);
+
+            Console.WriteLine($"Ore: {oreRequired}");
+        }
+
+        private static int GetRequiredOre(string reagentName, int amountRequired)
+        {
+            // Get the reaction to produce this reagent
+            var reaction = Reactions[reagentName];
+
+            // Get what we have already
+            var inInventory = Inventory[reagentName];
+
+            // Figure out how many reactions are needed
+            var reactionsRequired = (int)Math.Ceiling((decimal)Math.Max(amountRequired - inInventory, 0) / reaction.Result.Count);
+
+            // Set what we have in inventory after
+            Inventory[reagentName] = (reaction.Result.Count * reactionsRequired) - (amountRequired - inInventory);
+
+            var oreRequired = 0;
+
+            // Loop over each reagent
+            foreach (var reagent in reaction.Components)
+            {
+                if (reagent.Name == "ORE")
+                    oreRequired += reactionsRequired * reagent.Count;
+                else
+                    oreRequired += GetRequiredOre(reagent.Name, reagent.Count * reactionsRequired);
+            }
+
+            return oreRequired;
+        }
+    }
+}