diff --git a/src/main/scala/ninetyNineScalaProblems/Problem14.scala b/src/main/scala/ninetyNineScalaProblems/Problem14.scala
new file mode 100644
index 0000000..5c73893
--- /dev/null
+++ b/src/main/scala/ninetyNineScalaProblems/Problem14.scala
@@ -0,0 +1,18 @@
+package ninetyNineScalaProblems
+
+import scala.annotation.tailrec
+
+object Problem14:
+    def duplicateElements(list: List[Any]): List[Any] =
+        @tailrec
+        def loop(cursor: List[Any], acc: List[Any]): List[Any] =
+            cursor match
+                case e :: tail =>
+                    loop(tail, e :: e :: acc)
+                case Nil =>
+                    acc
+
+        loop(list, List()).reverse
+
+    def duplicateElements2(list: List[Any]): List[Any] =
+        list.flatMap(i => i :: List(i))
\ No newline at end of file
diff --git a/src/test/scala/ninetyNineScalaProblems/Problem14Suite.scala b/src/test/scala/ninetyNineScalaProblems/Problem14Suite.scala
new file mode 100644
index 0000000..9dc6ca4
--- /dev/null
+++ b/src/test/scala/ninetyNineScalaProblems/Problem14Suite.scala
@@ -0,0 +1,17 @@
+package ninetyNineScalaProblems
+
+import scala.compiletime.ops.boolean
+
+class Problem14Suite extends munit.FunSuite:
+    List(
+        (List(1, 2, 3, 4), List(1, 1, 2, 2, 3, 3, 4, 4)),
+        (List(1, 2, 2, 3), List(1, 1, 2, 2, 2, 2, 3, 3)),
+        (List(1, 2, 3, 2), List(1, 1, 2, 2, 3, 3, 2, 2)),
+        (List(), List()),
+        (List(1), List(1, 1)),
+        (List(1, 1, 1), List(1, 1, 1, 1, 1, 1)),
+    ).foreach:
+        case (list, expected) =>
+            test(s"duplicateElements returns [$expected]"):
+                assertEquals(Problem14.duplicateElements(list), expected)
+                assertEquals(Problem14.duplicateElements2(list), expected)
\ No newline at end of file