diff --git a/input/2021/day14-sample1.txt b/input/2021/day14-sample1.txt
new file mode 100644
index 0000000..b5594dd
--- /dev/null
+++ b/input/2021/day14-sample1.txt
@@ -0,0 +1,18 @@
+NNCB
+
+CH -> B
+HH -> N
+CB -> H
+NH -> C
+HB -> C
+HC -> B
+HN -> C
+NN -> C
+BH -> H
+NC -> B
+NB -> B
+BN -> B
+BB -> N
+BC -> B
+CC -> N
+CN -> C
diff --git a/input/2021/day14.txt b/input/2021/day14.txt
new file mode 100644
index 0000000..e84aae5
--- /dev/null
+++ b/input/2021/day14.txt
@@ -0,0 +1,102 @@
+SNPVPFCPPKSBNSPSPSOF
+
+CF -> N
+NK -> B
+SF -> B
+HV -> P
+FN -> S
+VV -> F
+FO -> F
+VN -> V
+PV -> P
+FF -> P
+ON -> S
+PB -> S
+PK -> P
+OO -> P
+SP -> F
+VF -> H
+OV -> C
+BN -> P
+OH -> H
+NC -> F
+BH -> N
+CS -> C
+BC -> N
+OF -> N
+SN -> B
+FP -> F
+FV -> K
+HP -> H
+VB -> P
+FH -> F
+HF -> P
+BB -> O
+HH -> S
+PC -> O
+PP -> B
+VS -> B
+HC -> H
+NS -> N
+KF -> S
+BO -> V
+NP -> S
+NF -> K
+BS -> O
+KK -> O
+VC -> V
+KP -> K
+CK -> P
+HN -> F
+KN -> H
+KH -> N
+SB -> S
+NO -> K
+HK -> H
+BF -> V
+SV -> B
+CV -> P
+CO -> P
+FC -> O
+CP -> H
+CC -> N
+CN -> P
+SK -> V
+SS -> V
+VH -> B
+OS -> N
+FB -> H
+NB -> N
+SC -> K
+NV -> H
+HO -> S
+SO -> P
+PH -> C
+VO -> O
+OB -> O
+FK -> S
+PN -> P
+VK -> O
+NH -> N
+OC -> B
+BP -> O
+PF -> F
+KB -> K
+KV -> B
+PO -> N
+NN -> K
+CH -> O
+KC -> P
+OP -> V
+VP -> F
+OK -> P
+FS -> K
+CB -> S
+HB -> N
+KS -> O
+BK -> C
+BV -> O
+SH -> H
+PS -> N
+HS -> K
+KO -> N
diff --git a/src/main/scala/de.qwertyuiop.aoc/2021/day11.scala b/src/main/scala/de.qwertyuiop.aoc/2021/day11.scala
index f5ff801..efd6d41 100644
--- a/src/main/scala/de.qwertyuiop.aoc/2021/day11.scala
+++ b/src/main/scala/de.qwertyuiop.aoc/2021/day11.scala
@@ -44,7 +44,7 @@ object Octopodes:
       if flashing.isEmpty then
         (f.view.mapValues(v => if v > 9 then 0 else v).toMap, flashed.size + flashing.size)
       else
-        val neighs = flashing.toVector.flatMap(_.neighbours).occurrences
+        val neighs = flashing.toVector.flatMap(_.neighbours).occurrences.mapValuesS(_.toInt)
         val newF = f.map((coord, v) => coord -> (
             if v > 9 || flashing.contains(coord) then 12
             else (v + neighs.getOrElse(coord, 0)).min(11)
diff --git a/src/main/scala/de.qwertyuiop.aoc/2021/day14.scala b/src/main/scala/de.qwertyuiop.aoc/2021/day14.scala
index 506abd4..8065e8d 100644
--- a/src/main/scala/de.qwertyuiop.aoc/2021/day14.scala
+++ b/src/main/scala/de.qwertyuiop.aoc/2021/day14.scala
@@ -3,4 +3,30 @@ package de.qwertyuiop.aoc.`2021`
 import de.qwertyuiop.aoc.lib.*
 import cats.*, cats.implicits.given
 
-def day14(using InputSource): Unit = ???
+def day14(using InputSource): Unit =
+  val (template :: "" :: rulesRaw) = input()
+  val rules = rulesRaw.flatMap(_.splitOnce(" -> ").map((pair, target) => pair -> (s"${pair.head}$target", s"$target${pair.tail}"))).toMap
+
+
+  def solve(part: Int, steps: Int) =
+    val occurrences = growPolymer(template, rules)(steps)
+    val max = occurrences.maxBy(_._2)
+    val min = occurrences.minBy(_._2)
+    println(s"Most common:  ${max}")
+    println(s"Least common: ${min}")
+    println(s"Solution Part $part: ${max._2 - min._2}")
+
+  solve(1,10)
+  solve(2,40)
+
+def growPolymer(start: String, rules: Map[String, (String, String)])(maxSteps: Int): Map[Char, Long] =
+  def growRec(pairs: Map[String, Long])(steps: Int): Map[String, Long] =
+    if steps == 0 then pairs
+    else
+      growRec(
+        pairs.toVector.foldMap{(pair, count) => val (a, b) = rules(pair); Map(a -> count, b -> count) }
+      )(steps - 1)
+
+  val pairCounts = growRec(start.sliding(2).toVector.occurrences)(maxSteps)
+    ++ Map(start.head.toString -> 1L, start.last.toString -> 1L)
+  pairCounts.toVector.foldMap((pair, count) => Map(pair.head -> count))
diff --git a/src/main/scala/de.qwertyuiop.aoc/lib/extensions.scala b/src/main/scala/de.qwertyuiop.aoc/lib/extensions.scala
index c613daa..27e7b46 100644
--- a/src/main/scala/de.qwertyuiop.aoc/lib/extensions.scala
+++ b/src/main/scala/de.qwertyuiop.aoc/lib/extensions.scala
@@ -10,7 +10,7 @@ extension [A](input: List[A])(using CanEqual[A,A])
           h #:: (if keepSeparator then tail else t).split(separator)
 
 extension [A](iterable: Iterable[A])
-  def occurrences: Map[A, Int] = iterable.groupMapReduce(identity)(_ => 1)(_ + _)
+  def occurrences: Map[A, Long] = iterable.groupMapReduce(identity)(_ => 1L)(_ + _)
 
 /* Using -Yexplicit-nulls isn't really ready for use with the java standard
  * library. e.g. String doesn't have `@NotNull` annotations for its methods