Problem 13

src/main/scala/ninetyNineScalaProblems/Problem13.scala

@@ -0,0 +1,19 @@
+package ninetyNineScalaProblems
+
+import scala.annotation.tailrec
+
+object Problem13:
+    def runLengthEncode(list: List[Any]): List[Tuple2[Int, Any]] =
+        @tailrec
+        def loop(cursor: List[Any], acc: List[Tuple2[Int, Any]]): List[Tuple2[Int, Any]] =
+            cursor match
+                case e :: tail =>
+                    acc match
+                        case (f, v) :: t if v == e =>
+                            loop(tail, (f + 1, v) :: t)
+                        case a =>
+                            loop(tail, (1, e) :: a)
+                case Nil =>
+                    acc
+
+        loop(list, List()).reverse

src/test/scala/ninetyNineScalaProblems/Problem13Suite.scala

@@ -0,0 +1,16 @@
+package ninetyNineScalaProblems
+
+import scala.compiletime.ops.boolean
+
+class Problem13Suite extends munit.FunSuite:
+    List(
+        (List(1, 2, 3, 4), List((1, 1), (1, 2), (1, 3), (1, 4))),
+        (List(1, 2, 2, 3), List((1, 1), (2, 2), (1, 3))),
+        (List(1, 2, 3, 2), List((1, 1), (1, 2), (1, 3), (1, 2))),
+        (List(), List()),
+        (List(1, 1, 1), List((3, 1))),
+        (List(1, 1, 1, 2), List((3, 1), (1, 2))),
+    ).foreach:
+        case (list, expected) =>
+            test(s"runLengthEncoding returns [$expected]"):
+                assertEquals(Problem13.runLengthEncode(list), expected)