[Typescript] 78. Medium - Unqiue

Implement the type version of Lodash.uniq, Unique takes an Array T, returns the Array T without repeated values.

type Res = Unique<[1, 1, 2, 2, 3, 3]>; // expected to be [1, 2, 3]
type Res1 = Unique<[1, 2, 3, 4, 4, 5, 6, 7]>; // expected to be [1, 2, 3, 4, 5, 6, 7]
type Res2 = Unique<[1, "a", 2, "b", 2, "a"]>; // expected to be [1, "a", 2, "b"]
type Res3 = Unique<[string, number, 1, "a", 1, string, 2, "b", 2, number]>; // expected to be [string, number, 1, "a", 2, "b"]
type Res4 = Unique<[unknown, unknown, any, any, never, never]>; // expected to be [unknown, any, never]

 

/* _____________ Your Code Here _____________ */

export type Equal<T, U> = 
  (<P>(x: P) => P extends T ? 1: 2) extends 
  (<P>(x: P) => P extends U ? 1: 2) 
    ? true
    : false;

export type IndexOf<T extends any[], U, ACC extends unknown[] = []> = T extends [infer F, ...infer RT]
  ? Equal<F, U> extends true
    ? ACC['length']
    : IndexOf<RT, U, [...ACC, unknown]>
  : -1;

export type Unique<T extends any[], ACC extends any[] = []> = T extends [infer F, ...infer RT]
  ? IndexOf<ACC, F> extends -1
    ? Unique<RT, [...ACC, F]>
    : Unique<RT, ACC>
  : ACC;

/* _____________ Test Cases _____________ */
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<Unique<[1, 1, 2, 2, 3, 3]>, [1, 2, 3]>>,
  Expect<Equal<Unique<[1, 2, 3, 4, 4, 5, 6, 7]>, [1, 2, 3, 4, 5, 6, 7]>>,
  Expect<Equal<Unique<[1, 'a', 2, 'b', 2, 'a']>, [1, 'a', 2, 'b']>>,
  Expect<Equal<Unique<[string, number, 1, 'a', 1, string, 2, 'b', 2, number]>, [string, number, 1, 'a', 2, 'b']>>,
  Expect<Equal<Unique<[unknown, unknown, any, any, never, never]>, [unknown, any, never]>>,
]