feat: complete day 2

04/CeresSearch.Tests/GridTests.cs

@@ -0,0 +1,56 @@
+namespace CeresSearch.Tests;
+
+public class GridTests
+{
+  private readonly string[] _exampleInput = [
+    "MMMSXXMASM",
+    "MSAMXMSMSA",
+    "AMXSXMAAMM",
+    "MSAMASMSMX",
+    "XMASAMXAMM",
+    "XXAMMXXAMA",
+    "SMSMSASXSS",
+    "SAXAMASAAA",
+    "MAMMMXMMMM",
+    "MXMXAXMASX",
+  ];
+
+  private async Task<string[]> GetPuzzleInput()
+  {
+    return await File.ReadAllLinesAsync(Path.Combine(AppContext.BaseDirectory, "INPUT.txt"));
+  }
+
+  [Test]
+  public async Task CountOccurrences_WhenCalledWithExampleInput_ItShouldReturnExpectedCount()
+  {
+    var result = new Grid(_exampleInput).CountOccurrences("XMAS");
+
+    await Assert.That(result).IsEqualTo(18);
+  }
+  
+  [Test]
+  public async Task CountOccurrences_WhenCalledWithPuzzleInput_ItShouldReturnExpectedCount()
+  {
+    var input = await GetPuzzleInput();
+    var result = new Grid(input).CountOccurrences("XMAS");
+
+    await Assert.That(result).IsEqualTo(2644);
+  }
+
+  [Test]
+  public async Task CountXmases_WhenCalledWithExampleInput_ItShouldReturnExpectedCount()
+  {
+    var result = new Grid(_exampleInput).CountXmases();
+
+    await Assert.That(result).IsEqualTo(9);
+  }
+  
+  [Test]
+  public async Task CountXmases_WhenCalledWithPuzzleInput_ItShouldReturnExpectedCount()
+  {
+    var input = await GetPuzzleInput();
+    var result = new Grid(input).CountXmases();
+
+    await Assert.That(result).IsEqualTo(1952);
+  }
+}

04/CeresSearch/Grid.cs

@@ -0,0 +1,154 @@
+using System.Xml;
+
+namespace CeresSearch;
+
+record Direction(int XOffset, int YOffset)
+{
+  public static readonly Direction Up = new(0, -1);
+  public static readonly Direction Down = new(0, 1);
+  public static readonly Direction Left = new(-1, 0);
+  public static readonly Direction Right = new(1, 0);
+  public static readonly Direction DownToTheRight = new(1, 1);
+  public static readonly Direction DownToTheLeft = new(-1, 1);
+  public static readonly Direction UpToTheRight = new(1, -1);
+  public static readonly Direction UpToTheLeft = new(-1, -1);
+}
+
+class Grid(string[] input)
+{
+  private readonly Direction[] _directions = [
+    Direction.UpToTheLeft,
+    Direction.UpToTheRight,
+    Direction.DownToTheLeft,
+    Direction.DownToTheRight,
+    Direction.Up,
+    Direction.Down,
+    Direction.Left,
+    Direction.Right,
+  ];
+
+  public int CountXmases()
+  {
+    var total = 0;
+    
+    WalkGrid((rowIndex, columnIndex) =>
+    {
+      if (FoundXmas(rowIndex, columnIndex))
+      {
+        total++;
+      }
+    });
+
+    return total;
+  }
+  
+  public int CountOccurrences(string word)
+  {
+    var total = 0;
+
+    WalkGrid((rowIndex, columnIndex) => 
+      total += _directions.Count(direction => FoundWord(word, direction, rowIndex, columnIndex))
+    );
+
+    return total;
+  }
+
+  private void WalkGrid(Action<int, int> callback)
+  {
+    for (var rowIndex = 0; rowIndex < input.Length; rowIndex++)
+    {
+      var row = input[rowIndex];
+      
+      for (var columnIndex = 0; columnIndex < row.Length; columnIndex++)
+      {
+        callback(rowIndex, columnIndex);
+      }
+    }
+  }
+
+  private bool FoundXmas(int rowIndex, int colIndex)
+  {
+    var currentCharacter = input[rowIndex][colIndex];
+
+    if (currentCharacter is not 'A')
+    {
+      return false;
+    }
+
+    var xmasMap = new Dictionary<Direction, char>();
+
+    foreach (var direction in _directions)
+    {
+      if (
+        direction == Direction.Up || 
+        direction == Direction.Down || 
+        direction == Direction.Left ||
+        direction == Direction.Right
+      )
+      {
+        continue;
+      }
+
+      var rowIndexToCheck = rowIndex + direction.XOffset;
+      var colIndexToCheck = colIndex + direction.YOffset;
+
+      if (IsOffGrid(rowIndexToCheck, colIndexToCheck))
+      {
+        return false;
+      }
+
+      var characterToCheck = input[rowIndexToCheck][colIndexToCheck];
+
+      if (characterToCheck != 'S' && characterToCheck != 'M')
+      {
+        return false;
+      }
+      
+      xmasMap.Add(direction, characterToCheck);
+    }
+
+    return IsValidXmas(xmasMap);
+  }
+
+  private bool IsValidXmas(Dictionary<Direction, char> map)
+  {
+    var upToTheRight = map[Direction.UpToTheRight];
+    var downToTheLeft = map[Direction.DownToTheLeft];
+    var upToTheLeft = map[Direction.UpToTheLeft];
+    var downToTheRight = map[Direction.DownToTheRight];
+    
+    return upToTheRight != downToTheLeft && upToTheLeft != downToTheRight;
+  }
+
+  private bool FoundWord(string word, Direction direction, int rowIndex, int columnIndex)
+  {
+    for (var currentTargetCharacterIndex = 0; currentTargetCharacterIndex < word.Length; currentTargetCharacterIndex++)
+    {
+      var currentTargetCharacter = word[currentTargetCharacterIndex];
+      var currentCharacterRowIndex = rowIndex + (direction.XOffset * currentTargetCharacterIndex);
+      var currentCharacterColumnIndex = columnIndex + (direction.YOffset * currentTargetCharacterIndex);
+      
+      if (IsOffGrid(currentCharacterRowIndex, currentCharacterColumnIndex))
+      {
+        return false;
+      }
+      
+      var currentCharacter = input[currentCharacterRowIndex][currentCharacterColumnIndex];
+
+      if (currentCharacter != currentTargetCharacter)
+      {
+        return false;
+      }
+    }
+    
+    return true;
+  }
+
+  private bool IsOffGrid(int rowIndex, int columnIndex)
+  {
+    return rowIndex < 0 ||
+           rowIndex > input.Length - 1 ||
+           columnIndex < 0 ||
+           columnIndex > input[0].Length - 1;
+  }
+}

04/CeresSearch/Program.cs

@@ -1,2 +1,30 @@
-// See https://aka.ms/new-console-template for more information
+using System.Diagnostics;
-Console.WriteLine("Hello, World!");
+
+using CeresSearch;
+
+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 grid = new Grid(input);
+
+var results = isPart2
+  ? grid.CountXmases()
+  : grid.CountOccurrences("XMAS");
+  
+stopwatch.Stop();
+Console.WriteLine($"The number of occurrences is {results}. ({stopwatch.ElapsedMilliseconds}ms)");