Add day 19

Days/Day19.cs

@@ -0,0 +1,179 @@
+using System.Collections.Frozen;
+using System.Numerics;
+using System.Runtime.Intrinsics.X86;
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day19 : Day
+{
+    public override int Number => 19;
+    public override string Name => "Linen Layout";
+
+    public override void RunPart1(bool display = true)
+    {
+        var (towels, patterns) = ParseInput();
+        var impossiblePatterns = new HashSet<string>();
+
+        var possiblePatterns = 0;
+
+        foreach (var pattern in patterns)
+        {
+            // Check if it's possible to make this pattern
+            if (CheckPattern(pattern))
+            {
+                possiblePatterns++;
+            }
+        }
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Number of designs that are possible: [yellow]{possiblePatterns}[/][/]");
+        }
+
+        return;
+
+        bool CheckPattern(ReadOnlySpan<char> pattern)
+        {
+            // Console.WriteLine($"Checking '{pattern}'");
+
+            if (pattern.Length is 0)
+            {
+                return true;
+            }
+
+            if (impossiblePatterns.Contains(pattern.ToString()))
+            {
+                return false;
+            }
+
+            var prefix = pattern[0];
+
+            if (!towels.TryGetValue(prefix, out var towelsList))
+            {
+                impossiblePatterns.Add(pattern.ToString());
+
+                return false;
+            }
+
+            foreach (var towel in towelsList)
+            {
+                if (pattern.StartsWith(towel) && CheckPattern(pattern[towel.Length..]))
+                {
+                    return true;
+                }
+            }
+
+            impossiblePatterns.Add(pattern.ToString());
+
+            return false;
+        }
+    }
+
+    public override void RunPart2(bool display = true)
+    {
+        var (towels, patterns) = ParseInput();
+        var impossiblePatterns = new HashSet<string>();
+        var knownPatterns = new Dictionary<string, long>();
+
+        var possibleCombinations = 0L;
+
+        foreach (var pattern in patterns)
+        {
+            // Check if it's possible to make this pattern
+            possibleCombinations += CheckPattern(pattern);
+        }
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Number of combinations that are possible: [yellow]{possibleCombinations}[/][/]");
+        }
+
+        return;
+
+        long CheckPattern(ReadOnlySpan<char> pattern)
+        {
+            if (pattern.Length is 0)
+            {
+                return 1;
+            }
+
+            if (impossiblePatterns.Contains(pattern.ToString()))
+            {
+                return 0;
+            }
+
+            if (knownPatterns.TryGetValue(pattern.ToString(), out var count))
+            {
+                return count;
+            }
+
+            var prefix = pattern[0];
+
+            if (!towels.TryGetValue(prefix, out var towelsList))
+            {
+                impossiblePatterns.Add(pattern.ToString());
+
+                return 0;
+            }
+
+            var possibilities = 0L;
+
+            foreach (var towel in towelsList)
+            {
+                if (pattern.StartsWith(towel))
+                {
+                    possibilities += CheckPattern(pattern[towel.Length..]);
+                }
+            }
+
+            if (possibilities is 0)
+            {
+                impossiblePatterns.Add(pattern.ToString());
+            }
+            else
+            {
+                knownPatterns.Add(pattern.ToString(), possibilities);
+            }
+
+            return possibilities;
+        }
+    }
+
+    private (FrozenDictionary<char, List<string>> Towels, List<string> Patterns) ParseInput()
+    {
+        var towels = new Dictionary<char, List<string>>();
+        var patterns = new List<string>();
+
+        foreach (var line in Input.AsSpan().EnumerateLines())
+        {
+            if (towels.Count is 0)
+            {
+                var split = line.Split(", ");
+
+                foreach (var range in split)
+                {
+                    var towel = line[range].Trim();
+
+                    var prefix = towel[0];
+
+                    if (!towels.TryGetValue(prefix, out var towelsList))
+                    {
+                        towelsList = [];
+                        towels[prefix] = towelsList;
+                    }
+
+                    towelsList.Add(towel.ToString());
+                }
+            }
+            else if (!line.IsWhiteSpace())
+            {
+                var pattern = line.Trim();
+
+                patterns.Add(pattern.ToString());
+            }
+        }
+
+        return (towels.ToFrozenDictionary(), patterns);
+    }
+}