00296-medium-permutation.ts

// ============= Test Cases =============
import type { Equal, Expect } from './test-utils'

type cases = [
  Expect<Equal<Permutation<'A'>, ['A']>>,
  Expect<Equal<Permutation<'A' | 'B' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
  Expect<Equal<Permutation<'B' | 'A' | 'C'>, ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']>>,
  Expect<Equal<Permutation<boolean>, [false, true] | [true, false]>>,
  Expect<Equal<Permutation<never>, []>>,
]


// ============= Your Code Here =============
type Permutation<T, U = T> = [T] extends [never] 
  ? [] 
  : T extends unknown
  ? [T, ...Permutation<Exclude<U, T>>] 
  : never;

type test1 = Permutation<boolean>
type test2 = Exclude<boolean, true>