From b7e700ad34eae8e300bd41870c831688e541c850 Mon Sep 17 00:00:00 2001
From: Martin Zikmund <martin@zikmund.dev>
Date: Fri, 20 Dec 2024 09:32:28 +0100
Subject: [PATCH] AoC 2024 Day 19 Solutions

---
 .../2024/19/Part1/Part1.cs                    | 41 +++++++++++++++++
 .../2024/19/Part2/Part2.cs                    | 44 +++++++++++++++++++
 src/AdventOfCode.Puzzles/2024/19/TestData.txt | 10 +++++
 3 files changed, 95 insertions(+)
 create mode 100644 src/AdventOfCode.Puzzles/2024/19/Part1/Part1.cs
 create mode 100644 src/AdventOfCode.Puzzles/2024/19/Part2/Part2.cs
 create mode 100644 src/AdventOfCode.Puzzles/2024/19/TestData.txt

diff --git a/src/AdventOfCode.Puzzles/2024/19/Part1/Part1.cs b/src/AdventOfCode.Puzzles/2024/19/Part1/Part1.cs
new file mode 100644
index 0000000..7c5dcb5
--- /dev/null
+++ b/src/AdventOfCode.Puzzles/2024/19/Part1/Part1.cs
@@ -0,0 +1,41 @@
+namespace AdventOfCode.Puzzles._2024._19.Part1;
+
+public partial class Part1 : IPuzzleSolution
+{
+    private string[] _patterns;
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        _patterns = (await inputReader.ReadLineAsync()).Split(", ");
+        await inputReader.ReadLineAsync();
+        int possibleCount = 0;
+        while (await inputReader.ReadLineAsync() is { } towel)
+        {
+            if (IsPossible("", towel))
+            {
+                possibleCount++;
+            }
+        }
+
+        return possibleCount.ToString();
+    }
+
+    private bool IsPossible(string current, string towel)
+    {
+        if (current == towel)
+        {
+            return true;
+        }
+
+        for (int i = 0; i < _patterns.Length; i++)
+        {
+            var newStart = current + _patterns[i];
+            if (towel.StartsWith(newStart) && IsPossible(newStart, towel))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}
diff --git a/src/AdventOfCode.Puzzles/2024/19/Part2/Part2.cs b/src/AdventOfCode.Puzzles/2024/19/Part2/Part2.cs
new file mode 100644
index 0000000..6753e5b
--- /dev/null
+++ b/src/AdventOfCode.Puzzles/2024/19/Part2/Part2.cs
@@ -0,0 +1,44 @@
+namespace AdventOfCode.Puzzles._2024._19.Part2;
+
+public partial class Part2 : IPuzzleSolution
+{
+    private HashSet<string> _patterns;
+
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        _patterns = new HashSet<string>((await inputReader.ReadLineAsync()).Split(", "));
+        await inputReader.ReadLineAsync();
+        ulong possibleCount = 0;
+        while (await inputReader.ReadLineAsync() is { } towel)
+        {
+            possibleCount += CountPossible(towel);
+        }
+
+        return possibleCount.ToString();
+    }
+
+    private ulong CountPossible(string towel)
+    {
+        ulong[] ways = new ulong[towel.Length + 1];
+        ways[0] = 1;
+
+        for (var length = 1; length <= towel.Length; length++)
+        {
+            for (int previousLength = 0; previousLength < length; previousLength++)
+            {
+                if (ways[previousLength] == 0)
+                {
+                    continue;
+                }
+
+                var current = towel.Substring(previousLength, length - previousLength);
+                if (_patterns.Contains(current))
+                {
+                    ways[length] += ways[previousLength];
+                }
+            }
+        }
+
+        return ways[towel.Length];
+    }
+}
diff --git a/src/AdventOfCode.Puzzles/2024/19/TestData.txt b/src/AdventOfCode.Puzzles/2024/19/TestData.txt
new file mode 100644
index 0000000..29648be
--- /dev/null
+++ b/src/AdventOfCode.Puzzles/2024/19/TestData.txt
@@ -0,0 +1,10 @@
+r, wr, b, g, bwu, rb, gb, br
+
+brwrr
+bggr
+gbbr
+rrbgbr
+ubwu
+bwurrg
+brgr
+bbrgwb