day 22

src/aoc/Year2024/Day22.cs

@@ -1,20 +1,67 @@
+using MoreLinq;
+
 namespace aoc.Year2024;
 
 internal partial class Day22
 {
-    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 long[] Parse(string input)
+	{
+		return Numerics.IntegerInt64.Lines().Parse(input);
+	}
+
+	private static IEnumerable<long> SecretSeq(long init)
+	{
+		return MoreEnumerable.Generate(init, current =>
+		{
+			current = ((current * 64) ^ current) % 16777216;
+			current = ((current / 32) ^ current) % 16777216;
+			current = ((current * 2048) ^ current) % 16777216;
+			return current;
+		});
+	}
+
+	internal partial class Part1
+	{
+		private readonly Example example = new(
+			"""
+			1
+			10
+			100
+			2024
+			""", 37327623);
+
+		public long Solve(long[] input)
+		{
+			return input.Select(n => SecretSeq(n).ElementAt(2000)).Sum();
+		}
+	}
+
+	internal partial class Part2
+	{
+		private readonly Example example = new(
+			"""
+			1
+			2
+			3
+			2024
+			""", 23L);
+
+		public long Solve(long[] input)
+		{
+			return input.Select(buyer => SecretSeq(buyer).Take(2001))
+				.SelectMany(CollectPricesAndChanges)
+				.GroupBy(x => x.changeSeq, x => x.price, (_, prices) => prices.Sum())
+				.Max();
+		}
+
+		private static IEnumerable<((long, long, long, long) changeSeq, long price)> CollectPricesAndChanges(IEnumerable<long> secret)
+		{
+			return secret.Select(x => x % 10)
+				.Window(5)
+				.Select(window => (
+					changeSeq: (window[1] - window[0], window[2] - window[1], window[3] - window[2], window[4] - window[3]),
+					price: window[4]
+				)).DistinctBy(x => x.changeSeq);
+		}
+	}
 }

tests/AoC.Tests/InputTests.cs

@@ -50,5 +50,7 @@ private static IEnumerable<PartInputCaseData> GetCases()
 		yield return new PartInputCaseData(20, 2, "1011325");
 		yield return new PartInputCaseData(21, 1, "169390");
 		yield return new PartInputCaseData(21, 2, "210686850124870");
+		yield return new PartInputCaseData(22, 1, "20401393616");
+		yield return new PartInputCaseData(22, 2, "2272");
 	}
 }