2024 Day19 Solved

Solutions/2024/Day19.cs

@@ -22,6 +22,11 @@ public static int Part1(string[] _)
 		.Where(design => design.IsPossible(_towelPatterns))
 		.Count();
 
+	public static long Part2(string[] _)
+		=> _desiredDesigns
+			.Select(design => design.AllPossible(_towelPatterns, []).Sum())
+			.Sum();
+
 	public static bool IsPossible(this string design, List<string> patterns)
 	{
 		if (design is "") {
@@ -37,5 +42,23 @@ public static bool IsPossible(this string design, List<string> patterns)
 		return false;
 	}
 
-	public static string Part2(string[] input, params object[]? args) => NO_SOLUTION_WRITTEN_MESSAGE;
+	public static IEnumerable<long> AllPossible(this string design, List<string> patterns, Dictionary<(string, string), long> cache)
+	{
+		if (design is "") {
+			yield return 1;
+			yield break;
+		}
+
+		foreach (string pattern in patterns.Where(design.StartsWith)) {
+			if (cache.TryGetValue((design, pattern), out long cacheCount)) {
+				yield return cacheCount;
+				continue;
+			}
+
+			List<long> count = [.. design[pattern.Length..].AllPossible(patterns, cache)];
+			long sum = count.Sum();
+			cache.Add((design, pattern), sum);
+			yield return sum;
+		}
+	}
 }

Tests/2024/Tests_19.cs

@@ -22,4 +22,59 @@ public void Part1(string input, int expected)
 		_ = int.TryParse(SolutionRouter.SolveProblem(YEAR, DAY, PART1, input), out int actual);
 		actual.ShouldBe(expected);
 	}
+
+	[Theory]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		brwrr
+		bggr
+		gbbr
+		rrbgbr
+		ubwu
+		bwurrg
+		brgr
+		bbrgwb
+		""", 16)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		ubwu
+		bbrgwb
+		""", 0)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		brwrr
+		""", 2)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		bggr
+		""", 1)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		gbbr
+		""", 4)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		rrbgbr
+		""", 6)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		bwurrg
+		""", 1)]
+	[InlineData("""
+		r, wr, b, g, bwu, rb, gb, br
+
+		brgr
+		""", 2)]
+	public void Part2(string input, int expected)
+	{
+		_ = int.TryParse(SolutionRouter.SolveProblem(YEAR, DAY, PART2, input), out int actual);
+		actual.ShouldBe(expected);
+	}
 }