Add ts filter challenge answer

Author: programandoconro

Languages/Typescript/Generics/18220-medium-filter.ts

@@ -0,0 +1,51 @@
+ /*
+    18220 - Filter
+    -------
+    by Muhun Kim (@x86chi) #medium #array #filter
+
+    ### Question
+
+    Implement the type `Filter<T, Predicate>` takes an Array `T`, primitive type or union primitive type `Predicate` and returns an Array include the elements of
+   `Predicate`.
+
+    > View on GitHub: https://tsch.js.org/18220
+  */
+
+  /* _____________ Your Code Here _____________ */
+
+  // My try
+
+  type Filter<T extends any[], P, Acc extends P[] = []> = T extends [infer F, ...infer R]
+  ? F extends P
+    ? Filter<R, P, [...Acc, F]>
+    : Filter<R, P, Acc>
+  : Acc
+
+  // A simplest option from other programmer (no accummulator)
+  
+  type Filter2<T extends unknown[], P> = T extends [infer F, ...infer R]
+    ? F extends P
+      ? [F, ...Filter<R, P>]
+      : Filter<R, P>
+    : [];
+
+
+  type Testo = Filter<[0, 1, 2], 0 | 1>    
+    //   ^? type Testo = [0, 1]
+  /* _____________ Test Cases _____________ */
+  import type { Equal, Expect } from '@type-challenges/utils'^M
+  
+  type Falsy = false | 0 | '' | null | undefined^M
+  
+  type cases = [
+    Expect<Equal<Filter<[0, 1, 2], 2>, [2]>>,^M
+    Expect<Equal<Filter<[0, 1, 2], 0 | 1>, [0, 1]>>,^M
+    Expect<Equal<Filter<[0, 1, 2], Falsy>, [0]>>,^M
+  ]
+
+  /* _____________ Further Steps _____________ */
+  /*
+    > Share your solutions: https://tsch.js.org/18220/answer
+    > View solutions: https://tsch.js.org/18220/solutions
+    > More Challenges: https://tsch.js.org
+  */