day 23

src/aoc/Year2024/Day23.cs

@@ -2,19 +2,102 @@ namespace aoc.Year2024;
 
 internal partial class Day23
 {
-    internal partial class Part1
-    {
-        public string Solve(string input)
-        {
-            throw new NotImplementedException();
-        }
-    }
-
-    internal partial class Part2
-    {
-        public string Solve(string input)
-        {
-            throw new NotImplementedException();
-        }
-    }
+	private IList<HashSet<string>> CollectGroups((string from, string to)[] input)
+	{
+		var d =
+			input.Concat(input.Select(x => (x.to, x.from)))
+				.GroupBy(x => x.Item1, x => x.Item2)
+				.ToDictionary(x => x.Key, x => x.ToHashSet());
+
+		var all = input.SelectMany(x => new[] { x.from, x.to })
+			.ToHashSet();
+
+		var groups = new List<HashSet<string>>();
+		foreach (var comp in all)
+		{
+			var matchingGroups = groups.Where(
+					group => group.IsSubsetOf(d[comp]))
+				.ToList();
+
+			foreach (var matchingGroup in matchingGroups)
+				groups.Add([..matchingGroup, comp]);
+
+			groups.Add([comp]);
+		}
+
+		return groups;
+	}
+
+	internal partial class Part1
+	{
+		public Part1()
+		{
+			Expect(example, 7);
+		}
+
+		public int Solve((string to, string from)[] input)
+		{
+			return CollectGroups(input)
+				.Count(group => group.Count == 3 && group.Any(g => g.StartsWith('t')));
+		}
+	}
+
+	internal partial class Part2
+	{
+		public Part2()
+		{
+			Expect(example, "co,de,ka,ta");
+		}
+
+		public string Solve((string from, string to)[] input)
+		{
+			var groups = CollectGroups(input);
+			return string.Join(",", groups.MaxBy(group => group.Count)!.Order());
+		}
+	}
+
+	public (string, string)[] Parse(string input)
+	{
+		return Character.Letter.Many()
+			.ThenIgnore(Span.EqualTo("-"))
+			.Then(Character.Letter.Many())
+			.Select(x => (new string(x.Item1), new string(x.Item2)))
+			.Lines().Parse(input);
+	}
+
+	private readonly Example example = new(
+		"""
+		kh-tc
+		qp-kh
+		de-cg
+		ka-co
+		yn-aq
+		qp-ub
+		cg-tb
+		vc-aq
+		tb-ka
+		wh-tc
+		yn-cg
+		kh-ub
+		ta-co
+		de-co
+		tc-td
+		tb-wq
+		wh-td
+		ta-ka
+		td-qp
+		aq-cg
+		wq-ub
+		ub-vc
+		de-ta
+		wq-aq
+		wq-vc
+		wh-yn
+		ka-de
+		kh-ta
+		co-tc
+		wh-qp
+		tb-vc
+		td-yn
+		""");
 }

tests/AoC.Tests/InputTests.cs

@@ -52,5 +52,7 @@ private static IEnumerable<PartInputCaseData> GetCases()
 		yield return new PartInputCaseData(21, 2, "210686850124870");
 		yield return new PartInputCaseData(22, 1, "20401393616");
 		yield return new PartInputCaseData(22, 2, "2272");
+		yield return new PartInputCaseData(23, 1, "1302");
+		yield return new PartInputCaseData(23, 2, "cb,df,fo,ho,kk,nw,ox,pq,rt,sf,tq,wi,xz");
 	}
 }