From 13487dcb421e34a54e106a12e734c00b045e9368 Mon Sep 17 00:00:00 2001
From: Jakob Scheid <jakob.scheid@icloud.com>
Date: Thu, 19 Mar 2026 15:39:26 +0100
Subject: [PATCH] Problem 12

---
 .../ninetyNineScalaProblems/Problem12.scala   | 19 +++++++++++++++++++
 .../Problem12Suite.scala                      | 16 ++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 src/main/scala/ninetyNineScalaProblems/Problem12.scala
 create mode 100644 src/test/scala/ninetyNineScalaProblems/Problem12Suite.scala

diff --git a/src/main/scala/ninetyNineScalaProblems/Problem12.scala b/src/main/scala/ninetyNineScalaProblems/Problem12.scala
new file mode 100644
index 0000000..d3da0ae
--- /dev/null
+++ b/src/main/scala/ninetyNineScalaProblems/Problem12.scala
@@ -0,0 +1,19 @@
+package ninetyNineScalaProblems
+
+import scala.annotation.tailrec
+import scala.annotation.constructorOnly
+
+object Problem12:
+    def runLengthDecode(list: List[Tuple2[Int, Any]]): List[Tuple2[Int, Any] | Any] =
+        @tailrec
+        def loop(cursor: List[Tuple2[Int, Any]], acc: List[Tuple2[Int, Any] | Any]): List[Tuple2[Int, Any] | Any] =
+            cursor match
+                case t :: tail =>
+                    t match
+                        case (f, v) if f > 1 =>
+                            loop((f - 1, v) :: tail, v :: acc)
+                        case (f, v) =>
+                            loop(tail, v :: acc)
+                case Nil => acc
+
+        loop(list, List()).reverse
\ No newline at end of file
diff --git a/src/test/scala/ninetyNineScalaProblems/Problem12Suite.scala b/src/test/scala/ninetyNineScalaProblems/Problem12Suite.scala
new file mode 100644
index 0000000..5569d0b
--- /dev/null
+++ b/src/test/scala/ninetyNineScalaProblems/Problem12Suite.scala
@@ -0,0 +1,16 @@
+package ninetyNineScalaProblems
+
+import scala.compiletime.ops.boolean
+
+class Problem12Suite extends munit.FunSuite:
+    List(
+        (List((1 ,1), (1, 2), (1, 3), (1, 4)), List(1, 2, 3, 4)),
+        (List(), List()),
+        (List((1, 1), (1, 2), (1, 3), (1, 2)), List(1, 2, 3, 2)),
+        (List((1, 1)), List(1)),
+        (List((2, 1)), List(1, 1)),
+        (List((4, 1), (1,2), (2, 3), (2, 1), (1, 4), (4, 5)), List(1, 1, 1, 1, 2, 3, 3, 1, 1, 4, 5, 5, 5, 5))
+    ).foreach:
+        case (list, expected) =>
+            test(s"runLengthDecode returns [$expected]"):
+                assertEquals(Problem12.runLengthDecode(list), expected)
\ No newline at end of file