Day 23

Having some serious grid/pathfinding fatigue here. Part 2 is slow, but, like...I'm fine with it.

advent-of-code-2023.csproj

@@ -75,6 +75,14 @@
 	  <EmbeddedResource Include="inputs\20b.txt" />
 	  <EmbeddedResource Include="inputs\21.txt" />
 	  <EmbeddedResource Include="inputs\21a.txt" />
+	  <None Remove="inputs\22.txt" />
+	  <EmbeddedResource Include="inputs\22.txt" />
+	  <None Remove="inputs\22a.txt" />
+	  <EmbeddedResource Include="inputs\22a.txt" />
+	  <None Remove="inputs\23.txt" />
+	  <EmbeddedResource Include="inputs\23.txt" />
+	  <None Remove="inputs\23a.txt" />
+	  <EmbeddedResource Include="inputs\23a.txt" />
 	</ItemGroup>
 
 	<ItemGroup>

inputs/23.txt

@@ -0,0 +1,141 @@
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+#...#...#...#.#.#.#.#.#.#...#...#.#.#.....#.#...#...#.#.#.#.#.#.#.#.#.#.#...#.#.#.#.....#...#.#.#.#...#...>.>.#...#...#...#...###...###.#.#.#
+###.#.#######.#.#.#.#.#.#########.#.#.#####.###.###.#.#.#.#.#.#.#.#.#.#.#.###.#.#.#.#####.#.#.#.#.###.#.#######.#####.#.#####.#########.#.#.#
+#...#.......#.#.#.#.#.#...#.......#.#.#...#.###.#...#.#.#.#.#.#.#.#.#.#.#...#.#.#.#...#...#.#.#.#.#...#.......#...#...#...#...#.........#.#.#
+#.#########.#.#.#.#.#.###.#.#######.#.#.#.#.###.#.###.#.#.#.#.#.#.#.#.#.###.#.#.#.###.#.###.#.#.#.#.#########.###.#.#####.#.###.#########.#.#
+#...........#...#...#.....#.........#...#...###...###...#...#...#...#...###...#...###...###...#...#...........###...#####...###...........#.#
+###########################################################################################################################################.#

inputs/23a.txt

@@ -0,0 +1,23 @@
+#.#####################
+#.......#########...###
+#######.#########.#.###
+###.....#.>.>.###.#.###
+###v#####.#v#.###.#.###
+###.>...#.#.#.....#...#
+###v###.#.#.#########.#
+###...#.#.#.......#...#
+#####.#.#.#######.#.###
+#.....#.#.#.......#...#
+#.#####.#.#.#########v#
+#.#...#...#...###...>.#
+#.#.#v#######v###.###v#
+#...#.>.#...>.>.#.###.#
+#####v#.#.###v#.#.###.#
+#.....#...#...#.#.#...#
+#.#########.###.#.#.###
+#...###...#...#...#.###
+###.###.#.###v#####v###
+#...#...#.#.>.>.#.>.###
+#.###.###.#.###.#.#v###
+#.....###...###...#...#
+#####################.#

src/23.cs

@@ -0,0 +1,251 @@
+using aoc2023.Util;
+
+namespace aoc2023;
+
+internal class Day23 : Day
+{
+    private IEnumerable<ivec2> GetNeighbors(ivec2 pos, bool oneWaySlopes = true)
+    {
+        if (grid[pos] != null && oneWaySlopes)
+        {
+            yield return (pos + grid[pos]!).Value;
+        }
+        else
+        {
+            foreach (var p in pos.GetOrthogonalNeighbors())
+            {
+                if (grid.ContainsKey(p))
+                {
+                    yield return p;
+                }
+            }
+        }
+    }
+
+    private int width;
+    private int height;
+    private readonly Dictionary<ivec2, ivec2?> grid = [];
+    private ivec2 start = ivec2.ZERO;
+    private ivec2 end = ivec2.ZERO;
+
+    internal override void Parse()
+    {
+        var lines = Parsing.ReadAllLines($"{GetDay()}").ToList();
+        height = lines.Count;
+        for (int row = 0; row < height; row++)
+        {
+            width = lines[row].Length;
+            for (int col = 0; col < width; col++)
+            {
+                if (lines[row][col] == '#')
+                {
+                    continue;
+                }
+
+                if (lines[row][col] == '.')
+                {
+                    var pt = new ivec2(col, row);
+                    grid.Add(pt, null);
+                    if (row == 0)
+                    {
+                        start = pt;
+                    }
+                    else if (row == height - 1)
+                    {
+                        end = pt;
+                    }
+                    continue;
+                }
+
+                grid.Add(new ivec2(col, row), lines[row][col] switch
+                {
+                    '>' => ivec2.RIGHT,
+                    '<' => ivec2.LEFT,
+                    '^' => ivec2.UP,
+                    'v' => ivec2.DOWN,
+                    _ => throw new Exception(),
+                });
+            }
+        }
+    }
+
+    private void Render(Dictionary<(ivec2, ivec2), int> visited)
+    {
+        for (int row = 0; row < height; row++)
+        {
+            for (int col = 0; col < width; col++)
+            {
+                var pt = new ivec2(col, row);
+                if (!grid.ContainsKey(pt))
+                {
+                    Logger.Log(Constants.SolidBlock.ToString());
+                    continue;
+                }
+
+                bool skip = false;
+                foreach (var v in visited)
+                {
+                    if (v.Key.Item1 == pt)
+                    {
+                        Logger.Log("O");
+                        skip = true;
+                        break;
+                    }
+                }
+
+                if (skip)
+                {
+                    continue;
+                }
+
+                if (grid[pt] == null)
+                {
+                    Logger.Log(" ");
+                    continue;
+                }
+
+                if (grid[pt] == ivec2.RIGHT)
+                {
+                    Logger.Log(">");
+                }
+                if (grid[pt] == ivec2.DOWN)
+                {
+                    Logger.Log("v");
+                }
+                if (grid[pt] == ivec2.UP)
+                {
+                    Logger.Log("^");
+                }
+                if (grid[pt] == ivec2.LEFT)
+                {
+                    Logger.Log("<");
+                }
+            }
+            Logger.LogLine("");
+        }
+    }
+
+    int GetLongestDistanceFrom(Dictionary<ivec2, List<(ivec2, int)>> graph, ivec2 pt, HashSet<ivec2> seen)
+    {
+        if (pt == end)
+        {
+            return 0;
+        }
+
+        var m = int.MinValue;
+        seen.Add(pt);
+        foreach (var pos in graph[pt])
+        {
+            if (!seen.Contains(pos.Item1))
+            {
+                m = System.Math.Max(m, GetLongestDistanceFrom(graph, pos.Item1, seen) + pos.Item2);
+            }
+        }
+
+        seen.Remove(pt);
+
+        return m;
+    }
+
+    internal override string Part1()
+    {
+        Dictionary<ivec2, List<(ivec2, int)>> graph = [];
+
+        HashSet<ivec2> forks = [start, end];
+        foreach (var pt in grid)
+        {
+            if (GetNeighbors(pt.Key).Count() >= 3)
+            {
+                forks.Add(pt.Key);
+                graph.Add(pt.Key, []);
+            }
+        }
+
+        HashSet<ivec2> seen = [];
+        foreach (var forkPoint in forks)
+        {
+            Stack<(ivec2, int)> s = [];
+            s.Push((forkPoint, 0));
+            seen.Clear();
+            seen.Add(forkPoint);
+
+            while (s.TryPop(out (ivec2 pos, int cost) next))
+            {
+                if (next.cost != 0 && forks.Contains(next.pos))
+                {
+                    graph.TryAdd(forkPoint, []);
+                    graph[forkPoint].Add((next.pos, next.cost));
+                    continue;
+                }
+
+                foreach (var neighbor in GetNeighbors(next.pos))
+                {
+                    if (seen.Contains(neighbor))
+                    {
+                        continue;
+                    }
+
+                    s.Push((neighbor, next.cost + 1));
+                    seen.Add(neighbor);
+                }
+            }
+        }
+
+        seen.Clear();
+        int dist = GetLongestDistanceFrom(graph, start, seen);
+
+        // Render();
+
+        return $"<+white>{dist}";
+    }
+
+    internal override string Part2()
+    {
+        Dictionary<ivec2, List<(ivec2, int)>> graph = [];
+
+        HashSet<ivec2> forks = [start, end];
+        foreach (var pt in grid)
+        {
+            if (GetNeighbors(pt.Key, false).Count() >= 3)
+            {
+                forks.Add(pt.Key);
+                graph.Add(pt.Key, []);
+            }
+        }
+
+        HashSet<ivec2> seen = [];
+        foreach (var forkPoint in forks)
+        {
+            Stack<(ivec2, int)> s = [];
+            s.Push((forkPoint, 0));
+            seen.Clear();
+            seen.Add(forkPoint);
+
+            while (s.TryPop(out (ivec2 pos, int cost) next))
+            {
+                if (next.cost != 0 && forks.Contains(next.pos))
+                {
+                    graph.TryAdd(forkPoint, []);
+                    graph[forkPoint].Add((next.pos, next.cost));
+                    continue;
+                }
+
+                foreach (var neighbor in GetNeighbors(next.pos, false))
+                {
+                    if (seen.Contains(neighbor))
+                    {
+                        continue;
+                    }
+
+                    s.Push((neighbor, next.cost + 1));
+                    seen.Add(neighbor);
+                }
+            }
+        }
+
+        seen.Clear();
+        int dist = GetLongestDistanceFrom(graph, start, seen);
+
+        return $"<+white>{dist}";
+    }
+}