[Typescript] 84. Medium - GetMiddleElement

Get the middle element of the array by implementing a GetMiddleElement method, represented by an array

If the length of the array is odd, return the middle element If the length of the array is even, return the middle two elements

For example

  type simple1 = GetMiddleElement<[1, 2, 3, 4, 5]>, // expected to be [3]
  type simple2 = GetMiddleElement<[1, 2, 3, 4, 5, 6]> // expected to be [3, 4]

 

/* _____________ Your Code Here _____________ */

type GetMiddleElement<T extends any[]> = T extends [infer L, ...infer Mid, infer R]
  ? Mid['length'] extends 0
    ? [L, R]
    : Mid['length'] extends 1 | 2
      ? Mid
      : GetMiddleElement<Mid>
  : T;

// Solution 2
type GetMiddleElement<T extends any[]> = T['length'] extends 0 | 1 | 2
  ? T
  : T extends [infer L, ...infer Mid, infer R]
    ? GetMiddleElement<Mid>
    : never;


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

type cases = [
  Expect<Equal<GetMiddleElement<[]>, []>>,
  Expect<Equal<GetMiddleElement<[1, 2, 3, 4, 5]>, [3]>>,
  Expect<Equal<GetMiddleElement<[1, 2, 3, 4, 5, 6]>, [3, 4]>>,
  Expect<Equal<GetMiddleElement<[() => string]>, [() => string]>>,
  Expect<Equal<GetMiddleElement<[() => number, '3', [3, 4], 5]>, ['3', [3, 4]]>>,
  Expect<Equal<GetMiddleElement<[() => string, () => number]>, [() => string, () => number]>>,
  Expect<Equal<GetMiddleElement<[never]>, [never]>>,
]
// @ts-expect-error
type error = GetMiddleElement<1, 2, 3>