Day 14 - Part 2

Day14/Day14.cs

@@ -10,14 +10,14 @@ namespace Advent
         private class Reagent
         {
             public string Name { get; }
-            public int Count { get; }
+            public long Count { get; }
 
             public Reagent(string s)
             {
                 var parts = s.Split(' ');
 
                 Name = parts[1];
-                Count = int.Parse(parts[0]);
+                Count = long.Parse(parts[0]);
             }
         }
 
@@ -42,7 +42,7 @@ namespace Advent
         }
 
         private static readonly Dictionary<string, Reaction> Reactions = new Dictionary<string, Reaction>();
-        private static readonly Dictionary<string, int> Inventory = new Dictionary<string, int>();
+        private static readonly Dictionary<string, long> Inventory = new Dictionary<string, long>();
 
         public static void Execute()
         {
@@ -53,30 +53,46 @@ namespace Advent
                 var reaction = new Reaction(line);
 
                 Reactions[reaction.Result.Name] = reaction;
-
-                Inventory[reaction.Result.Name] = 0;
             }
 
             var oreRequired = GetRequiredOre("FUEL", 1);
 
             Console.WriteLine($"Ore: {oreRequired}");
+
+            // Too lazy to do a binary search - find a decent starting point and go from there.  It finished
+            // in the few minutes it took to get coffee - good enough!
+
+            const long oreLimit = 1000000000000;
+            var fuel = (long)Math.Floor((decimal)oreLimit / oreRequired);
+
+            while (true)
+            {
+                oreRequired = GetRequiredOre("FUEL", fuel);
+
+                if (oreRequired > oreLimit)
+                    break;
+
+                fuel++;
+            }
+
+            Console.WriteLine($"Fuel: {fuel - 1}");
         }
 
-        private static int GetRequiredOre(string reagentName, int amountRequired)
+        private static long GetRequiredOre(string reagentName, long amountRequired)
         {
             // Get the reaction to produce this reagent
             var reaction = Reactions[reagentName];
 
             // Get what we have already
-            var inInventory = Inventory[reagentName];
+            var inInventory = Inventory.ContainsKey(reagentName) ? Inventory[reagentName] : 0;
 
             // Figure out how many reactions are needed
-            var reactionsRequired = (int)Math.Ceiling((decimal)Math.Max(amountRequired - inInventory, 0) / reaction.Result.Count);
+            var reactionsRequired = (long)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;
+            var oreRequired = 0L;
 
             // Loop over each reagent
             foreach (var reagent in reaction.Components)