feat: begin working on day 10 solution

10/HoofIt.Tests/TopoMapTests.cs

@@ -0,0 +1,44 @@
+namespace HoofIt.Tests;
+
+public class TopoMapTests
+{
+  private readonly string[] _exampleInput = [
+    "89010123",
+    "78121874",
+    "87430965",
+    "96549874",
+    "45678903",
+    "32019012",
+    "01329801",
+    "10456732",
+  ];
+  
+  [Test]
+  public async Task From_WhenCalled_ItShouldReturnNewInstanceOfTopoMap()
+  {
+    var result = TopoMap.From(_exampleInput);
+
+    await Assert.That(result).IsTypeOf<TopoMap>();
+  }
+
+  [Test]
+  public async Task GetTrailHeadScores_WhenCalledWithExampleInput_ItShouldReturnExpectedValues()
+  {
+    var expectedValues = new List<int>()
+    {
+      5,
+      6,
+      5,
+      3,
+      1,
+      3,
+      5,
+      3,
+      5,
+    };
+
+    var result = TopoMap.From(_exampleInput).GetTrailHeadScores();
+    
+    await Assert.That(result).IsEqualTo(36);
+  }
+}

10/HoofIt/Program.cs

@@ -1,2 +1,151 @@
-// See https://aka.ms/new-console-template for more information
-Console.WriteLine("Hello, World!");
+using System.Diagnostics;
+
+if (args.Length is 0)
+{
+  Console.WriteLine("Please provide a path to the input file.");
+  return;
+}
+
+if (File.Exists(args[0]) is false)
+{
+  Console.WriteLine("The provided file does not exist.");
+  return;
+}
+
+var isPart2 = args.Length is 2 && args[1] is "part2";
+var input = await File.ReadAllLinesAsync(args[0]);
+
+var stopwatch = new Stopwatch();
+stopwatch.Start();
+
+var map = TopoMap.From(input);
+
+// i'm going to to walk over the grid
+// i'm going to only worry about places where
+// there is a zero
+
+// need to check if we are on a nine
+// before we explore...also we should
+// be able to add to score here
+
+// when i encounter a zero i need to begin
+// exploring nearby tiles that increment by 1
+// in each left, right, up, down direction
+// any adj tile that fits this...is a tile i
+// need to also explore
+
+stopwatch.Stop();
+Console.WriteLine($". ({stopwatch.ElapsedMilliseconds}ms)");
+
+class TopoMap
+{
+  private static Direction[] _directions = [
+    Direction.Up,
+    Direction.Down,
+    Direction.Left,
+    Direction.Right,
+  ];
+  
+  private readonly string[] _grid;
+
+  private TopoMap(string[] input)
+  {
+    _grid = input;
+  }
+
+  public static TopoMap From(string[] input) => new(input);
+
+  // TODO: This actually needs to be GetTrailHeadScore
+  // I want to perform this search when I know I've reached
+  // a trail head.
+  public int GetTrailHeadScores()
+  {
+    var trailheadScore = 0;
+    var visitedPositions = new HashSet<Position>();
+    var positionsToVisit = new Queue<Position>();
+
+    var startingX = 0;
+    var startingY = 0;
+    var startingHeight = int.Parse(_grid[startingY][startingX].ToString());
+    positionsToVisit.Enqueue(new(startingX, startingY, startingHeight));
+
+    while (positionsToVisit.Count != 0)
+    {
+      var currentPosition = positionsToVisit.Dequeue();
+      
+      if (visitedPositions.Contains(currentPosition))
+      {
+        continue;
+      }
+
+      visitedPositions.Add(currentPosition);
+      
+      if (currentPosition.Height is 9)
+      {
+        trailheadScore++;
+        continue;
+      }
+
+      foreach (var direction in _directions)
+      {
+        if (currentPosition.TryGetNextPosition(direction, _grid, out var newPosition) is false)
+        {
+          continue;
+        }
+
+        if (visitedPositions.Contains(newPosition))
+        {
+          continue;
+        }
+
+        var heightDifference = newPosition.Height - currentPosition.Height;
+
+        if (heightDifference is not 1)
+        {
+          continue;
+        }
+        
+        positionsToVisit.Enqueue(newPosition);
+      }
+    }
+    
+    return trailheadScore;
+  }
+}
+
+record Position(int X, int Y, int Height)
+{
+  public bool TryGetNextPosition(Direction direction, string[] grid, out Position position)
+  {
+    var x = X + direction.XD;
+    var y = Y + direction.YD;
+
+    position = new(x, y, -1);
+
+    var isOffGrid = IsOffGrid(position, grid);
+
+    if (isOffGrid)
+    {
+      return false;
+    }
+
+    position = position with { Height = grid[y][x] };
+    return true;
+  }
+  
+  private bool IsOffGrid(Position position, string[] grid)
+  {
+    return position.X < 0 ||
+           position.X > grid[0].Length - 1 ||
+           position.Y > grid.Length - 1 ||
+           position.Y < 0;
+  }
+}
+
+record Direction(int XD, int YD)
+{
+  public static Direction Up = new(0, -1);
+  public static Direction Down = new(0, 1);
+  public static Direction Left = new(-1, 0);
+  public static Direction Right = new(1, 0);
+}