day 12 part 2

KaterynaKateryna · Dec 12, 2024 · ac172e1 · ac172e1
1 parent e5d8c7d
commit ac172e1
Showing 1 changed file with 186 additions and 12 deletions.
diff --git a/AdventOfCode/Day12.cs b/AdventOfCode/Day12.cs
@@ -1,7 +1,4 @@
-using System.Collections;
-using System.Collections.Generic;
-
-namespace AdventOfCode;
+namespace AdventOfCode;
 
 public class Day12 : BaseDay
 {
@@ -13,6 +10,16 @@ public Day12()
     }
 
     public override ValueTask<string> Solve_1()
+    {
+        return new(Solve(false).ToString());
+    }
+
+    public override ValueTask<string> Solve_2()
+    {
+        return new(Solve(true).ToString());
+    }
+
+    private int Solve(bool updated)
     {
         bool[][] visited = new bool[_input.Length][];
         for (int i = 0; i < visited.Length; ++i)
@@ -29,14 +36,11 @@ public override ValueTask<string> Solve_1()
             nextStart = GetNextNotVisited(visited);
         }
 
-        int price = areas.Sum(GetAreaPrice);
-
-        return new(price.ToString());
-    }
-
-    public override ValueTask<string> Solve_2()
-    {
-        return new("");
+        if (updated)
+        {
+            return areas.Sum(GetNewAreaPrice);
+        }
+        return areas.Sum(GetAreaPrice);
     }
 
     private List<Point> GetArea(Point start, bool[][] visited)
@@ -82,6 +86,166 @@ private int GetAreaPrice(List<Point> area)
         return perimeter * areaSize;
     }
 
+    private int GetNewAreaPrice(List<Point> area)
+    {
+        int areaSize = area.Count;
+
+        HashSet<PointSide> sides = new HashSet<PointSide>();
+
+        foreach (Point point in area)
+        {
+            // top
+            if (point.I == 0 || !area.Contains(new Point(point.I - 1, point.J)))
+            {
+                TryAddSide(point, Side.Top, sides, area);
+            }
+
+            // bottom
+            if (point.I == _input.Length - 1 || !area.Contains(new Point(point.I + 1, point.J)))
+            {
+                TryAddSide(point, Side.Bottom, sides, area);
+            }
+
+            // left
+            if (point.J == 0 || !area.Contains(new Point(point.I, point.J - 1)))
+            {
+                TryAddSide(point, Side.Left, sides, area);
+            }
+
+            // right
+            if (point.J == _input[0].Length || !area.Contains(new Point(point.I, point.J + 1)))
+            {
+                TryAddSide(point, Side.Right, sides, area);
+            }
+        }
+
+        return sides.Count * areaSize;
+    }
+
+    private void TryAddSide(Point point, Side side, HashSet<PointSide> pointSides, List<Point> area)
+    {
+        if (side == Side.Top || side == Side.Bottom)
+        {
+            var existingSides = pointSides.Where(ps => ps.Point.I == point.I && ps.Side == side);
+            foreach (var existing in existingSides)
+            {
+                if (CanReachHorizontally(point, existing, side))
+                {
+                    return;
+                }
+            }
+            pointSides.Add(new PointSide(point, side));
+        }
+
+        if (side == Side.Left || side == Side.Right)
+        {
+            var existingSides = pointSides.Where(ps => ps.Point.J == point.J && ps.Side == side);
+            foreach (var existing in existingSides)
+            {
+                if (CanReachVertically(point, existing, side))
+                {
+                    return;
+                }
+            }
+            pointSides.Add(new PointSide(point, side));
+        }
+    }
+
+    private bool CanReachHorizontally(Point point, PointSide existing, Side side)
+    {
+        char value = _input[point.I][point.J];
+        if (point.J < existing.Point.J)
+        {
+            for (int j= point.J + 1; j < existing.Point.J; ++j)
+            {
+                if (_input[point.I][j] != value)
+                {
+                    return false;
+                }
+                if (side == Side.Top && point.I != 0 && _input[point.I - 1][j] == value)
+                {
+                    return false;
+                }
+                if (side == Side.Bottom && point.I != _input.Length - 1 && _input[point.I + 1][j] == value)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        if (point.J > existing.Point.J)
+        {
+            for (int j = point.J - 1; j > existing.Point.J; --j)
+            {
+                if (_input[point.I][j] != value)
+                {
+                    return false;
+                }
+                if (side == Side.Top && point.I != 0 && _input[point.I - 1][j] == value)
+                {
+                    return false;
+                }
+                if (side == Side.Bottom && point.I != _input.Length - 1 && _input[point.I + 1][j] == value)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        throw new Exception();
+    }
+
+    private bool CanReachVertically(Point point, PointSide existing, Side side)
+    {
+        char value = _input[point.I][point.J];
+        if (point.I < existing.Point.I)
+        {
+            for (int i = point.I + 1; i < existing.Point.I; ++i)
+            {
+                if (_input[i][point.J] != value)
+                {
+                    return false;
+                }
+                if (side == Side.Left && point.J != 0 && _input[i][point.J - 1] == value)
+                {
+                    return false;
+                }
+                if (side == Side.Right && point.J != _input[i].Length - 1 && _input[i][point.J + 1] == value)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        if (point.I > existing.Point.I)
+        {
+            for (int i = point.I - 1; i > existing.Point.I; --i)
+            {
+                if (_input[i][point.J] != value)
+                {
+                    return false;
+                }
+                if (side == Side.Left && point.J != 0 && _input[i][point.J - 1] == value)
+                {
+                    return false;
+                }
+                if (side == Side.Right && point.J != _input[i].Length - 1 && _input[i][point.J + 1] == value)
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
+
+        throw new Exception();
+    }
 
     private Point? GetNextNotVisited(bool[][] visited)
     {
@@ -126,4 +290,14 @@ private IEnumerable<Point> GetNeighbourPoints(Point current)
     }
 
     private record Point(int I, int J);
+
+    private enum Side
+    { 
+        Top,
+        Bottom,
+        Left,
+        Right
+    }
+
+    private record PointSide(Point Point, Side Side);
 }