day 5

src/aoc/Year2024/Day05/Day05.cs

@@ -2,19 +2,121 @@ namespace aoc.Year2024.Day05;
 
 internal partial class Day05
 {
-    internal partial class Part1
-    {
-        public string Solve(string input)
-        {
-            throw new NotImplementedException();
-        }
-    }
-
-    internal partial class Part2
-    {
-        public string Solve(string input)
-        {
-            throw new NotImplementedException();
-        }
-    }
+	public record Page(List<int> Numbers)
+	{
+		public static Page Create(IEnumerable<int> numbers) => new(numbers.ToList());
+
+		public int? FindIndex(int number)
+		{
+			var index = Numbers.IndexOf(number);
+			return index == -1 ? null : index;
+		}
+
+		public int Middle() => Numbers[Numbers.Count / 2];
+	}
+
+	public record Rule(int Smaller, int Larger)
+	{
+		public static Rule Create(int smaller, int larger) => new(smaller, larger);
+
+		public bool Satisfied(Page page)
+		{
+			var smallerIndex = page.FindIndex(Smaller);
+			var largerIndex = page.FindIndex(Larger);
+			if (smallerIndex is null || largerIndex is null)
+				return true;
+			return smallerIndex < largerIndex;
+		}
+	}
+
+	public static (Rule[] rules, Page[] pages) ParseInput(string input)
+	{
+		var rulesParser =
+			Numerics.IntegerInt32.ThenIgnore(Span.EqualTo("|"))
+				.Then(Numerics.IntegerInt32)
+				.Select(Rule.Create)
+				.Lines();
+
+		var pages =
+			Numerics.IntegerInt32.ManyDelimitedBy(Span.EqualTo(","))
+				.Select(Page.Create)
+				.Lines();
+
+		return rulesParser.Block().ThenBlock(pages).Parse(input);
+	}
+
+	internal partial class Part1
+	{
+		private readonly Example example = new(ExampleInput, 143);
+
+		public int Solve((Rule[] rules, Page[] pages) input)
+		{
+			var correctPages 
+				= input.pages.Where(page => input.rules.All(rule => rule.Satisfied(page)));
+			return correctPages.Select(x => x.Middle()).Sum();
+		}
+
+		public (Rule[] rules, Page[] pages) Parse(string input) => ParseInput(input);
+	}
+
+	internal partial class Part2
+	{
+		private readonly Example example = new(ExampleInput, 123);
+
+		public int Solve((Rule[] rules, Page[] pages) input)
+		{
+			var incorrectPages
+				= input.pages.Where(page => ! input.rules.All(rule => rule.Satisfied(page)));
+
+			return incorrectPages.Select(page =>
+				Page.Create(page.Numbers.Order(new Comparer(input.rules))).Middle())
+				.Sum();
+		}
+
+		private class Comparer(Rule[] rules) : IComparer<int>
+		{
+			public int Compare(int x, int y)
+			{
+				if (rules.Contains(Rule.Create(x, y)))
+					return 1;
+				if (rules.Contains(Rule.Create(y, x)))
+					return -1;
+				return 0;
+			}
+		}
+
+		public (Rule[] rules, Page[] pages) Parse(string input) => ParseInput(input);
+	}
+
+	private const string ExampleInput =
+		"""
+		47|53
+		97|13
+		97|61
+		97|47
+		75|29
+		61|13
+		75|53
+		29|13
+		97|29
+		53|29
+		61|53
+		97|53
+		61|29
+		47|13
+		75|47
+		97|75
+		47|61
+		75|61
+		47|29
+		75|13
+		53|13
+
+		75,47,61,53,29
+		97,61,53,29,13
+		75,29,13
+		75,97,47,61,53
+		61,13,29
+		97,13,75,29,47
+		""";
 }

tests/AoC.Tests/InputTests.cs

@@ -16,5 +16,7 @@ private static IEnumerable<PartInputCaseData> GetCases()
 		yield return new PartInputCaseData(3, 2, "99532691");
 		yield return new PartInputCaseData(4, 1, "2646");
 		yield return new PartInputCaseData(4, 2, "2000");
+		yield return new PartInputCaseData(5, 1, "5639");
+		yield return new PartInputCaseData(5, 2, "5273");
 	}
 }