diff --git a/advent-of-typescript/2023/day_15.ts b/advent-of-typescript/2023/day_15.ts
new file mode 100644
index 0000000..81a165f
--- /dev/null
+++ b/advent-of-typescript/2023/day_15.ts
@@ -0,0 +1,29 @@
+import { Equal, Expect } from "type-testing";
+
+/* -----------------------------------------------------------------------------------------------
+ * Code Here
+ * -----------------------------------------------------------------------------------------------*/
+
+type BoxToys<S, N, Arr extends S[] = []> =
+  // Arr["length"] extends N // this doesn't work w/ union types
+  N extends Arr["length"] // works
+    ? Arr
+    : BoxToys<S, N, [...Arr, S]>;
+
+/* -----------------------------------------------------------------------------------------------
+ * Do Not Edit Below This Line
+ * -----------------------------------------------------------------------------------------------*/
+
+type test_doll_actual = BoxToys<"doll", 1>;
+//   ^?
+type test_doll_expected = ["doll"];
+type test_doll = Expect<Equal<test_doll_expected, test_doll_actual>>;
+
+type test_nutcracker_actual = BoxToys<"nutcracker", 3 | 4>;
+//   ^?
+type test_nutcracker_expected =
+  | ["nutcracker", "nutcracker", "nutcracker"]
+  | ["nutcracker", "nutcracker", "nutcracker", "nutcracker"];
+type test_nutcracker = Expect<
+  Equal<test_nutcracker_expected, test_nutcracker_actual>
+>;