Day 10 part 2 - ugly AF implementation

Day10/Grid.cs

@@ -7,9 +7,9 @@ public class Grid
     private readonly int _width;
     private readonly int _height;
     private Tile? _start;
-    public Tile?[,] Tiles { get; }
+    public Tile[,] Tiles { get; }
 
-    public Grid(Tile?[,] tiles, int width, int height)
+    public Grid(Tile[,] tiles, int width, int height)
     {
         _width = width;
         _height = height;
@@ -23,7 +23,7 @@ public class Grid
             var lineBuilder = new StringBuilder();
             for (var x = 0; x < _width; x++)
             {
-                lineBuilder.Append(Tiles[x, y]?.Display ?? " ");
+                lineBuilder.Append(Tiles[x, y].Display ?? " ");
             }
             Console.WriteLine(lineBuilder);
         }
@@ -33,7 +33,7 @@ public class Grid
     {
         foreach (var t in Tiles)
         {
-            if (t?.Pipe == 'S')
+            if (t.Pipe == 'S')
             {
                 _start = t;
                 break;
@@ -44,7 +44,6 @@ public class Grid
             throw new Exception("Start is not set yet");
         }
         var queue = new Queue<(Tile Tile, GridPoint Source, int Index)>();
-        var num = 0;
         queue.Enqueue((_start, _start.Position, 0));
 
         while (queue.Count > 0)
@@ -53,6 +52,7 @@ public class Grid
             
             if (tile.HasDisplay)
             {
+                UpdateStart();
                 return index;
             }
             
@@ -65,16 +65,61 @@ public class Grid
             }
             
             tile.SetDisplay(index);
+        }
+
+        throw new Exception("No cycle found");
+    }
 
-            num++;
-            if (num % 100 == 0)
+    public int Enclosed()
+    {
+        var enclosed = 0;
+        for (var y = 0; y < _height; y++)
+        {
+            var verticals = 0;
+            var half = 0;
+            for (var x = 0; x < _width; x++)
             {
-                Print();
-                Console.WriteLine();
+                var tile = Tiles[x, y];
+                if (!tile.HasDisplay)
+                {
+                    enclosed += (verticals % 2 == 1) ? 1 : 0;
+                }
+                else
+                {
+                    switch (tile.Pipe)
+                    {
+                        case '|':
+                            verticals++;
+                            break;
+                        case 'F':
+                        case '7':
+                            half += 1;
+                            if (half == 0)
+                            {
+                                verticals++;
+                            }
+                            break;
+                        case 'J':
+                        case 'L':
+                            half -= 1;
+                            if (half == 0)
+                            {
+                                verticals++;
+                            }
+                            break;
+                        default:
+                            break;
+                    }
+
+                    if (Math.Abs(half) > 1)
+                    {
+                        half = 0;
+                    }
+                }
             }
         }
 
-        throw new Exception("No cycle found");
+        return enclosed;
     }
 
     public Tile? this[GridPoint point]
@@ -89,4 +134,54 @@ public class Grid
             return Tiles[point.X, point.Y];
         }
     }
+
+    private void UpdateStart()
+    {
+        var outlets = _start!
+            .GetConnections()
+            .Select(p => this[p])
+            .Where(t => (t?.HasDisplay ?? false) && (t.ConnectsTo(_start.Position)))
+            .Cast<Tile>()
+            .ToList();
+
+        if (outlets.Count != 2)
+        {
+            throw new Exception("Only 2 outlets for S expected");
+        }
+
+        var east = outlets.Any(t => t.Position.X > _start.Position.X);
+        var west = outlets.Any(t => t.Position.X < _start.Position.X);
+        var north = outlets.Any(t => t.Position.Y < _start.Position.Y);
+        var south = outlets.Any(t => t.Position.Y > _start.Position.Y);
+
+        var pipe = ' ';
+        if (north && south)
+        {
+            pipe = '|';
+        }
+        if (north && east)
+        {
+            pipe = 'L';
+        }
+        if (north && west)
+        {
+            pipe = 'J';
+        }
+        if (east && west)
+        {
+            pipe = '-';
+        }
+        if (south && east)
+        {
+            pipe = 'F';
+        }
+        if (south && west)
+        {
+            pipe = '7';
+        }
+
+        Tiles[_start.Position.X, _start.Position.Y] = new Tile(pipe, _start.Position);
+        _start = Tiles[_start.Position.X, _start.Position.Y];
+        _start.SetDisplay(0);
+    }
 }

Day10/Program.cs

@@ -21,5 +21,10 @@ var grid = parser.Parse(inputFile);
 var count = grid.Follow();
 Console.WriteLine();
 Console.WriteLine($"Steps: {count}");
+grid.Print();
+
+var enclosed = grid.Enclosed();
+Console.WriteLine();
+Console.WriteLine($"Enclosed: {enclosed}");
 
 return 0;