docs: add xml comments

04/Scratchcards.Tests/PuzzleSolverTests.cs

@@ -12,24 +12,49 @@ public class PuzzleSolverTests
     result.Should().Be(expected);
   }
 
+  [Theory]
+  [MemberData(nameof(TestData.GetTotalCardCountData), MemberType = typeof(TestData))]
+  public void GetTotalCardCount_GivenCards_ItShouldReturnExpectedValue(string[] cards, int expected)
+  {
+    var result = _sut.GetTotalCardCount(cards);
+    result.Should().Be(expected);
+  }
+
   public static class TestData
   {
+    private static readonly string[] ExampleInput =
+    [
+      "Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53",
+      "Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19",
+      "Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1",
+      "Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83",
+      "Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36",
+      "Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11",
+    ];
+
     private static string[] Input => File.ReadAllLines("INPUT.txt");
 
+    public static IEnumerable<object[]> GetTotalCardCountData =>
+      new List<object[]>
+      {
+        new object[]
+        {
+          ExampleInput,
+          30,
+        },
+        new object[]
+        {
+          Input,
+          5920640,
+        },
+      };
+
     public static IEnumerable<object[]> SumCardValuesData =>
       new List<object[]>
       {
         new object[]
         {
-          new[]
+          ExampleInput,
-          {
-            "Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53",
-            "Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19",
-            "Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1",
-            "Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83",
-            "Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36",
-            "Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11",
-          },
           13,
         },
         new object[]

04/Scratchcards/Program.cs

@@ -19,40 +19,116 @@ public class Program
     var puzzleSolver = new PuzzleSolver();
 
     var input = await File.ReadAllLinesAsync(args[0]);
-    var result = puzzleSolver.SumCardValues(input);
+    var result = args.Length is 2 && args[1] == "part2"
+      ? puzzleSolver.GetTotalCardCount(input)
+      : puzzleSolver.SumCardValues(input);
 
-    Console.WriteLine($"The sum of all card values is {result}.");
+    if (args.Length is 2 && args[1] == "part2")
+    {
+      Console.WriteLine($"The total number of cards is {result}.");
+    }
+    else
+    {
+      Console.WriteLine($"The total value of the cards is {result}.");
+    }
 
     return result;
   }
 }
 
+/// <summary>
+/// Solves the puzzle.
+/// </summary>
 public class PuzzleSolver
 {
+  /// <summary>
+  /// Sums the value of the cards.
+  /// </summary>
+  /// <param name="cards">The cards.</param>
+  /// <returns>The sum of the cards.</returns>
   public int SumCardValues(string[] cards) => cards
     .Select(Card.Parse)
     .Sum(c => c.GetCardValue());
+
+  /// <summary>
+  /// Gets the total number of cards.
+  /// </summary>
+  /// <param name="cards">The cards.</param>
+  /// <returns>The total number of cards.</returns>
+  public int GetTotalCardCount(string[] cards)
+  {
+    var cardStringsToProcess = new List<string>(cards);
+
+    for (var i = 0; i < cardStringsToProcess.Count; i++)
+    {
+      var currentCardString = cardStringsToProcess[i];
+      var currentCardStringIndex = Array.IndexOf(cards, currentCardString);
+      var currentCard = Card.Parse(currentCardString);
+      var numOfMatchingNumbersForCurrentCard = currentCard.MatchingNumbers.Count;
+      var cardIndexesToCopy = Enumerable.Range(
+        currentCardStringIndex + 1,
+        Math.Min(
+          numOfMatchingNumbersForCurrentCard,
+          cards.Length - currentCardStringIndex - 1
+        )
+      );
+
+      foreach (var index in cardIndexesToCopy)
+      {
+        cardStringsToProcess.Add(cards[index]);
+      }
+    }
+
+    return cardStringsToProcess.Count;
+  }
 }
 
+/// <summary>
+/// Represents a card.
+/// </summary>
+/// <param name="id">The identifier.</param>
+/// <param name="winningNumbers">The winning numbers.</param>
+/// <param name="numbers">The numbers.</param>
+/// <returns>An instance of <see cref="Card"/>.</returns>
 public class Card(
   int id,
   List<int> winningNumbers,
   List<int> numbers
 )
 {
+  /// <summary>
+  /// Gets the identifier.
+  /// </summary>
   public int Id { get; init; } = id;
+
+  /// <summary>
+  /// Gets the winning numbers.
+  /// </summary>
   public List<int> WinningNumbers { get; init; } = winningNumbers;
+
+  /// <summary>
+  /// Gets the numbers.
+  /// </summary>
   public List<int> Numbers { get; init; } = numbers;
 
-  public int GetCardValue()
+  /// <summary>
-  {
+  /// Gets the matching numbers.
-    var commonNumbers = WinningNumbers.Intersect(Numbers).ToList();
+  /// </summary>
+  public List<int> MatchingNumbers => Numbers.Intersect(WinningNumbers).ToList();
 
-    return commonNumbers.Count is 1
+  /// <summary>
-      ? 1
+  /// Gets the value of the card.
-      : (int)Math.Pow(2, commonNumbers.Count - 1);
+  /// </summary>
-  }
+  /// <returns>The value of the card.</returns>
+  public int GetCardValue() => MatchingNumbers.Count is 1
+    ? 1
+    : (int)Math.Pow(2, MatchingNumbers.Count - 1);
 
+  /// <summary>
+  /// Parses the specified input.
+  /// </summary>
+  /// <param name="input">The input.</param>
+  /// <returns>An instance of <see cref="Card"/>.</returns>
   public static Card Parse(string input)
   {
     var parts = input.Split(':');

README.md

@@ -40,7 +40,7 @@ dotnet run -- <path-to-input-file> part2
 | 01  | [Problem](./01/PROBLEM.md) |   [Solution](./01/Trebuchet/)   |   ✅   | The trickiest part here was accounting for overlapping digit words. |
 | 02  | [Problem](./02/PROBLEM.md) | [Solution](./02/CubeConundrum/) |   ✅   | The key to me here was to parse the input into a useful model.      |
 | 03  | [Problem](./03/PROBLEM.md) |  [Solution](./03/GearRatios/)   |   ✅   | The edge case that got me here was lines ending with a part number. |
-| 04  | [Problem](./04/PROBLEM.md) | [Solution](./04/Scratchcards/)  |   ⌛   |
+| 04  | [Problem](./04/PROBLEM.md) | [Solution](./04/Scratchcards/)  |   ✅   | Part 2 gets out of hand quickly with just 200 cards.                |
 | 05  | [Problem](./05/PROBLEM.md) |        [Solution](./05/)        |   ⌛   |
 | 06  | [Problem](./06/PROBLEM.md) |        [Solution](./06/)        |   ⌛   |
 | 07  | [Problem](./07/PROBLEM.md) |        [Solution](./07/)        |   ⌛   |