Merge pull request #19 from MartinZikmund/feature/aoc2024-day18

AoC 2024 Day 18 Solutions

src/AdventOfCode.Puzzles/2024/18/Part1/Part1.cs

@@ -0,0 +1,60 @@
+namespace AdventOfCode.Puzzles._2024._18.Part1;
+
+public partial class Part1 : IPuzzleSolution
+{
+    private const int Width = 71;
+    private const int Height = 71;
+    private const int ByteCount = 1024;
+
+    private char[,] _map = new char[Width, Height];
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        _map = new char[Width, Height];
+        for (int i = 0; i < ByteCount; i++)
+        {
+            var line = await inputReader.ReadLineAsync();
+            var parts = line.Split(",");
+            var x = int.Parse(parts[0]);
+            var y = int.Parse(parts[1]);
+
+            _map[x, y] = '#';
+        }
+
+        var length = FindPath((0,0), (Width - 1, Height - 1));
+
+        return length.ToString();
+    }
+
+    private int FindPath(Point start, Point end)
+    {
+        var queue = new Queue<(Point position, int steps)>();
+        queue.Enqueue((start, 0));
+        var visited = new HashSet<Point>();
+        visited.Add(start);
+        while (queue.Count > 0)
+        {
+            var (position, steps) = queue.Dequeue();
+            if (position == end)
+            {
+                return steps;
+            }
+
+            foreach (var direction in Directions.WithoutDiagonals)
+            {
+                var next = position + direction;
+                if ((next.X < 0 || next.X >= Width || next.Y < 0 || next.Y >= Height) ||
+                    (_map[next.X, next.Y] == '#') ||
+                    visited.Contains(next))
+                {
+                    continue;
+                }
+
+                visited.Add(next);
+                queue.Enqueue((next, steps + 1));
+            }
+        }
+
+        return -1;
+    }
+}

src/AdventOfCode.Puzzles/2024/18/Part2/Part2.cs

@@ -0,0 +1,76 @@
+namespace AdventOfCode.Puzzles._2024._18.Part2;
+
+public partial class Part2 : IPuzzleSolution
+{
+    private const int Width = 71;
+    private const int Height = 71;
+    private const int ByteCount = 1024;
+
+    private char[,] _map = new char[Width, Height];
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        _map = new char[Width, Height];
+        HashSet<Point> lastPath = new();
+        for (int i = 0; ; i++)
+        {
+            var line = await inputReader.ReadLineAsync();
+            var parts = line.Split(",");
+            var x = int.Parse(parts[0]);
+            var y = int.Parse(parts[1]);
+
+            _map[x, y] = '#';
+            if (lastPath.Count == 0 || lastPath.Contains((x, y)))
+            {
+                (var length, lastPath) = FindPath((0, 0), (Width - 1, Height - 1));
+
+                if (length == -1)
+                {
+                    return x + "," + y;
+                }
+            }
+        }
+    }
+
+    private (int length, HashSet<Point> points) FindPath(Point start, Point end)
+    {
+        var queue = new Queue<(Point position, int steps)>();
+        queue.Enqueue((start, 0));
+        var visited = new HashSet<Point>();
+        var previous = new Dictionary<Point, Point>();
+        visited.Add(start);
+        while (queue.Count > 0)
+        {
+            var (position, steps) = queue.Dequeue();
+            if (position == end)
+            {
+                var path = new HashSet<Point>();
+                var current = position;
+                while (current != start)
+                {
+                    path.Add(current);
+                    current = previous[current];
+                }
+
+                return (steps, path);
+            }
+
+            foreach (var direction in Directions.WithoutDiagonals)
+            {
+                var next = position + direction;
+                if ((next.X < 0 || next.X >= Width || next.Y < 0 || next.Y >= Height) ||
+                    (_map[next.X, next.Y] == '#') ||
+                    visited.Contains(next))
+                {
+                    continue;
+                }
+
+                visited.Add(next);
+                previous[next] = position;
+                queue.Enqueue((next, steps + 1));
+            }
+        }
+
+        return (-1, null);
+    }
+}

src/AdventOfCode.Puzzles/2024/18/TestData.txt

@@ -0,0 +1,25 @@
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0