add day 18

18/index.ts

@@ -0,0 +1,59 @@
+import { Expect, Equal } from "type-testing";
+
+type Count<
+  Toys extends string[],
+  Toy extends string,
+  Counts extends string[] = [],
+> = Toys extends [infer First, ...infer Rest extends string[]]
+  ? First extends Toy
+    ? Count<Rest, Toy, [...Counts, "1"]>
+    : Count<Rest, Toy, Counts>
+  : Counts["length"];
+
+// ------------------- Test section ---------------------
+
+// prettier-ignore
+type ToySack = [
+	'🎸', '🎧', '👟', '👟', '💻', '🪀', '🧩', '🎮',
+	'🎨', '🕹️', '📱', '🧩', '🧸', '🎧', '👟', '🚲',
+	'📚', '⌚', '🎨', '👟', '🎸', '🧸', '👟', '🎸',
+	'📱', '🎧', '🎮', '🎒', '📱', '🧩', '🧩', '🚲',
+	'🕹️', '🧵', '📱', '🕹️', '🕰️', '🧢', '🕹️', '👟',
+	'🧸', '📚', '🧁', '🧩', '🎸', '🎮', '🧁', '📚',
+	'💻', '⌚', '🛹', '🧁', '🧣', '🪁', '🎸', '🧸',
+	'🧸', '🧸', '🧩', '🪁', '🏎️', '🏎️', '🧁', '📚',
+	'🧸', '🕶️', '💻', '⌚', '⌚', '🕶️', '🎧', '🎧',
+	'🎧', '💻', '👟', '🎸', '💻', '🪐', '📚', '🎨',
+	'📱', '🎧', '📱', '🎸', '🏎️', '👟', '🚲', '📱',
+	'🚲', '🎸'
+];
+
+type test_0_actual = Count<ToySack, "👟">;
+//   ^?
+type test_0_expected = 8;
+type test_0 = Expect<Equal<test_0_expected, test_0_actual>>;
+
+type test_1_actual = Count<ToySack, "🧦">;
+//   ^?
+type test_1_expected = 0;
+type test_1 = Expect<Equal<test_1_expected, test_1_actual>>;
+
+type test_2_actual = Count<ToySack, "🧩">;
+//   ^?
+type test_2_expected = 6;
+type test_2 = Expect<Equal<test_2_expected, test_2_actual>>;
+
+type test_3_actual = Count<ToySack, "🛹">;
+//   ^?
+type test_3_expected = 1;
+type test_3 = Expect<Equal<test_3_expected, test_3_actual>>;
+
+type test_4_actual = Count<ToySack, "🏎️">;
+//   ^?
+type test_4_expected = 3;
+type test_4 = Expect<Equal<test_4_expected, test_4_actual>>;
+
+type test_5_actual = Count<ToySack, "📚">;
+//   ^?
+type test_5_expected = 5;
+type test_5 = Expect<Equal<test_5_expected, test_5_actual>>;