Merge pull request #30 from MartinZikmund/feature/aoc2025-day4

Author: MartinZikmund

src/AdventOfCode.Puzzles/2025/03/Part2/AoC2025Day3Part2.cs

@@ -1,6 +1,6 @@
 namespace AdventOfCode.Puzzles._2025._03.Part2;
 
-public class AoC2025Day3Part2 : IPuzzleSolution
+public class AoC2025Day4Part2 : IPuzzleSolution
 {
     public async Task<string> SolveAsync(StreamReader inputReader)
     {

src/AdventOfCode.Puzzles/2025/04/Part1/AoC2025Day4Part1.cs

@@ -0,0 +1,60 @@
+
+namespace AdventOfCode.Puzzles._2025._04.Part1;
+
+public class AoC2025Day4Part1 : IPuzzleSolution
+{
+    private const char Roll = '@';
+    private char[,] _map;
+    private int _width;
+    private int _height;
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        var lines = await inputReader.ReadAllLinesAsync();
+        _width = lines[0].Length;
+        _height = lines.Count;
+        _map = new char[lines[0].Length, lines.Count];
+        for (int x = 0; x < _width; x++)
+        {
+            for (int y = 0; y < _height; y++)
+            {
+                _map[x, y] = lines[y][x];
+            }
+        }
+
+        int movable = 0;
+        for (int y = 0; y < _height; y++)
+        {
+            for (int x = 0; x < _width; x++)
+            {
+                if (_map[x, y] == Roll && IsMovable(x, y))
+                {
+                    movable++;
+                }
+            }
+        }
+
+        return movable.ToString();
+    }
+
+    private bool IsMovable(int x, int y)
+    {
+        var adjacentRolls = 0;
+        foreach (var direction in Directions.WithDiagonals)
+        {
+            var neighborPosition = new Point(x + direction.X, y + direction.Y);
+            if (neighborPosition.X < 0 || neighborPosition.X >= _width ||
+                neighborPosition.Y < 0 || neighborPosition.Y >= _height)
+            {
+                continue;
+            }
+
+            if (_map[neighborPosition.X, neighborPosition.Y] == Roll)
+            {
+                adjacentRolls++;
+            }
+        }
+
+        return adjacentRolls < 4;
+    }
+}

src/AdventOfCode.Puzzles/2025/04/Part2/AoC2025Day4Part2.cs

@@ -0,0 +1,81 @@
+namespace AdventOfCode.Puzzles._2025._04.Part2;
+
+public class AoC2025Day4Part2 : IPuzzleSolution
+{
+    private const char Roll = '@';
+    private char[,] _map;
+    private int _width;
+    private int _height;
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        var lines = await inputReader.ReadAllLinesAsync();
+        _width = lines[0].Length;
+        _height = lines.Count;
+        _map = new char[lines[0].Length, lines.Count];
+        for (int x = 0; x < _width; x++)
+        {
+            for (int y = 0; y < _height; y++)
+            {
+                _map[x, y] = lines[y][x];
+            }
+        }
+
+        var total = 0;
+        while (true)
+        {
+            var movablePositions = FindMovable();
+            if (movablePositions.Length == 0)
+            {
+                break;
+            }
+
+            total += movablePositions.Length;
+
+            foreach (var pos in movablePositions)
+            {
+                _map[pos.X, pos.Y] = '.';
+            }
+        }
+
+        return total.ToString();
+    }
+
+    private Point[] FindMovable()
+    {
+        var positions = new List<Point>();
+        for (int y = 0; y < _height; y++)
+        {
+            for (int x = 0; x < _width; x++)
+            {
+                if (_map[x, y] == Roll && IsMovable(x, y))
+                {                    
+                    positions.Add(new Point(x, y));
+                }
+            }
+        }
+
+        return positions.ToArray();
+    }
+
+    private bool IsMovable(int x, int y)
+    {
+        var adjacentRolls = 0;
+        foreach (var direction in Directions.WithDiagonals)
+        {
+            var neighborPosition = new Point(x + direction.X, y + direction.Y);
+            if (neighborPosition.X < 0 || neighborPosition.X >= _width ||
+                neighborPosition.Y < 0 || neighborPosition.Y >= _height)
+            {
+                continue;
+            }
+
+            if (_map[neighborPosition.X, neighborPosition.Y] == Roll)
+            {
+                adjacentRolls++;
+            }
+        }
+
+        return adjacentRolls < 4;
+    }
+}

src/AdventOfCode.Puzzles/2025/04/TestData.txt

@@ -0,0 +1,10 @@
+..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.