Day 14 initial solution

Part 1 brute force, part 2 solved "correctly" (I think, anyway). This day runs slower than I would expect, given how little part 2 is doing.

advent-of-code-2021.csproj

@@ -57,6 +57,9 @@
 	  <None Update="inputs\13.txt">
 	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 	  </None>
+	  <None Update="inputs\14.txt">
+	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+	  </None>
 	</ItemGroup>
 
 </Project>

inputs/14.txt

@@ -0,0 +1,102 @@
+OKSBBKHFBPVNOBKHBPCO
+
+CB -> P
+VH -> S
+CF -> P
+OV -> B
+CH -> N
+PB -> F
+KF -> O
+BC -> K
+FB -> F
+SN -> F
+FV -> B
+PN -> K
+SF -> V
+FN -> F
+SS -> K
+VP -> F
+VB -> B
+OS -> N
+HP -> O
+NF -> S
+SK -> H
+OO -> S
+PF -> C
+CC -> P
+BP -> F
+OB -> C
+CS -> N
+BV -> F
+VV -> B
+HO -> F
+KN -> P
+VC -> K
+KK -> N
+BO -> V
+NH -> O
+HC -> S
+SB -> F
+NN -> V
+OF -> V
+FK -> S
+OP -> S
+NS -> C
+HV -> O
+PC -> C
+FO -> H
+OH -> F
+BF -> S
+SO -> O
+HB -> P
+NK -> H
+NV -> C
+NB -> B
+FF -> B
+BH -> C
+SV -> B
+BK -> K
+NO -> C
+VN -> P
+FC -> B
+PH -> V
+HH -> C
+VO -> O
+SP -> P
+VK -> N
+CP -> H
+SC -> C
+KV -> H
+CO -> C
+OK -> V
+ON -> C
+KS -> S
+NP -> O
+CK -> C
+BS -> F
+VS -> B
+KH -> O
+KC -> C
+KB -> N
+OC -> F
+PP -> S
+HK -> H
+BN -> S
+KO -> K
+NC -> B
+PK -> K
+CV -> H
+PO -> O
+BB -> C
+HS -> F
+SH -> K
+CN -> S
+HN -> S
+KP -> O
+FP -> H
+HF -> F
+PS -> B
+FH -> K
+PV -> O
+FS -> N
+VF -> V

src/14.cs

@@ -0,0 +1,109 @@
+using System.Text;
+
+namespace aoc2021;
+
+internal class Day14 : Day
+{
+    internal override void Go()
+    {
+        var lines = Util.ReadAllLines("inputs/14.txt");
+
+        string template = string.Empty;
+        Dictionary<string, char> rules = new();
+        foreach (var line in lines)
+        {
+            if (string.IsNullOrEmpty(template))
+            {
+                template = line;
+            }
+            else if (!string.IsNullOrEmpty(line))
+            {
+                var pair = line.Split(" -> ");
+                rules.Add(pair[0], pair[1][0]);
+            }
+        }
+
+        Part1(template, rules);
+        Part2(template, rules);
+    }
+
+    private static void Part1(string template, Dictionary<string, char> rules)
+    {
+        using var t = new Timer();
+
+        string curr = template;
+
+        for (int i = 0; i < 10; i++)
+        {
+            StringBuilder sb = new();
+            for (int j = 0; j < curr.Length - 1; j++)
+            {
+                sb.Append(curr[j]);
+                sb.Append(rules[curr[j..(j + 2)]]);
+            }
+            sb.Append(curr[curr.Length - 1]);
+            curr = sb.ToString();
+        }
+
+        Dictionary<char, int> frequency = new();
+        foreach (var c in curr)
+        {
+            if (!frequency.ContainsKey(c))
+            {
+                frequency.Add(c, 0);
+            }
+
+            frequency[c]++;
+        }
+        var least = frequency.MinBy(x => x.Value);
+        var most = frequency.MaxBy(x => x.Value);
+
+        Logger.Log($"part1: <blue>{most.Value - least.Value}<r>");
+    }
+
+    private static void Part2(string template, Dictionary<string, char> rules)
+    {
+        using var t = new Timer();
+
+        Dictionary<string, long> pairs = new();
+        Dictionary<char, long> frequencies = new();
+        foreach (var pair in rules)
+        {
+            pairs.Add(pair.Key, 0);
+            if (!frequencies.ContainsKey(pair.Key[0]))
+            {
+                frequencies.Add(pair.Key[0], 0);
+            }
+            if (!frequencies.ContainsKey(pair.Key[1]))
+            {
+                frequencies.Add(pair.Key[1], 0);
+            }
+        }
+        for (int i = 0; i < template.Length - 1; i++)
+        {
+            var pair = template[i..(i + 2)];
+            pairs[pair]++;
+            frequencies[template[i]]++;
+        }
+        frequencies[template[^1]]++;
+
+        for (int round = 0; round < 40; round++)
+        {
+            foreach (var pair in pairs.Where(x => x.Value > 0).ToList())
+            {
+                pairs[pair.Key] -= pair.Value;
+                frequencies[rules[pair.Key]] += pair.Value;
+
+                var np1 = $"{pair.Key[0]}{rules[pair.Key]}";
+                var np2 = $"{rules[pair.Key]}{pair.Key[1]}";
+                pairs[np1] += pair.Value;
+                pairs[np2] += pair.Value;
+            }
+        }
+
+        var least = frequencies.MinBy(x => x.Value);
+        var most = frequencies.MaxBy(x => x.Value);
+
+        Logger.Log($"part2: <blue>{most.Value - least.Value}<r>");
+    }
+}

src/main.cs

@@ -31,7 +31,8 @@ else
         "10" => new Day10(),
         "11" => new Day11(),
         "12" => new Day12(),
-        _ => new Day13(),
+        "13" => new Day13(),
+        _ => new Day14(),
     };
     day.Go();
 }