Day 10

🎵 All I need for Advent is my ivec2, my ivec2, my ivec2...

src/10.cs

@@ -0,0 +1,119 @@
+using aoc2024.Util;
+
+namespace aoc2024;
+
+internal class Day10 : Day
+{
+    int[][] grid = new int[10][];
+    internal override void Parse()
+    {
+        var lines = Util.Parsing.ReadAllLines($"{GetDay()}").ToList();
+        grid = new int[lines.Count][];
+        for (int y = 0; y < lines.Count; y++)
+        {
+            var row = new int[lines[y].Length];
+            for (int x = 0; x < row.Length; x++)
+            {
+                try
+                {
+                    row[x] = int.Parse(lines[y][x].ToString());
+                }
+                catch
+                {
+                    // support example inputs with '.' as part of the path
+                    row[x] = -1;
+                }
+            }
+
+            grid[y] = row;
+        }
+    }
+
+    internal override string Part1()
+    {
+        Queue<(ivec2 pos, ivec2 start)> paths = [];
+        Dictionary<ivec2, HashSet<ivec2>> trails = [];
+        for (int y = 0; y < grid.Length; y++)
+        {
+            for (int x = 0; x < grid[y].Length; x++)
+            {
+                if (grid[y][x] == 0)
+                {
+                    paths.Enqueue((new ivec2(x, y), new ivec2(x, y)));
+                }
+            }
+        }
+
+        while (paths.TryDequeue(out var segment))
+        {
+            foreach (var pt in segment.pos.GetBoundedOrthogonalNeighbors(0, 0, grid[0].Length - 1, grid.Length - 1))
+            {
+                if (grid[pt.y][pt.x] != grid[segment.pos.y][segment.pos.x] + 1)
+                {
+                    continue;
+                }
+
+                if (grid[pt.y][pt.x] == 9)
+                {
+                    if (!trails.TryAdd(segment.start, [pt]))
+                    {
+                        trails[segment.start].Add(pt);
+                    }
+
+                    continue;
+                }
+
+                paths.Enqueue((pt, segment.start));
+            }
+        }
+
+        return $"Trailhead scores sum: <+white>{trails.Sum(t => t.Value.Count)}";
+    }
+
+    internal override string Part2()
+    {
+        Queue<(ivec2 pos, ivec2 start)> paths = [];
+        Dictionary<ivec2, Dictionary<ivec2, int>> trails = [];
+        for (int y = 0; y < grid.Length; y++)
+        {
+            for (int x = 0; x < grid[y].Length; x++)
+            {
+                if (grid[y][x] == 0)
+                {
+                    paths.Enqueue((new ivec2(x, y), new ivec2(x, y)));
+                }
+            }
+        }
+
+        while (paths.TryDequeue(out var segment))
+        {
+            foreach (var pt in segment.pos.GetBoundedOrthogonalNeighbors(0, 0, grid[0].Length - 1, grid.Length - 1))
+            {
+                if (grid[pt.y][pt.x] != grid[segment.pos.y][segment.pos.x] + 1)
+                {
+                    continue;
+                }
+
+                if (grid[pt.y][pt.x] == 9)
+                {
+                    if (!trails.TryGetValue(segment.start, out var value))
+                    {
+                        value = [];
+                        trails.Add(segment.start, value);
+                    }
+
+                    if (!value.TryAdd(pt, 1))
+                    {
+                        value[pt]++;
+                    }
+
+                    continue;
+                }
+
+                paths.Enqueue((pt, segment.start));
+            }
+        }
+
+        return $"Trailhead ratings sum: <+white>{trails.Sum(t => t.Value.Sum(e => e.Value))}";
+    }
+}