4518-fill.ts

/**
 * 4518 - Fill
 *
 * `Fill`, a common JavaScript function, now let us implement it with types.
 * `Fill<T, N, Start?, End?>`, as you can see,`Fill` accepts four types of parameters, of which `T` and `N` are required parameters, and `Start` and `End` are optional parameters.
 * The requirements for these parameters are: `T` must be a `tuple`, `N` can be any type of value, `Start` and `End` must be integers greater than or equal to 0.
 *
 * ```ts
 * type exp = Fill<[1, 2, 3], 0> // expected to be [0, 0, 0]
 * ```
 * In order to simulate the real function, the test may contain some boundary conditions, I hope you can enjoy it :)
 *
 *
 */

/* _____________ Your Code Here _____________ */

type Fill<
  T extends unknown[],
  N,
  Start extends number = 0,
  End extends number = T['length'],
  C extends unknown[] = [],
  Flag extends boolean = C['length'] extends Start ? true : false
> = C['length'] extends End
  ? T
  : T extends [infer A, ...infer R]
    ? Flag extends true
      ? [N, ...Fill<R, N, Start, End, [...C, 0], Flag>]
      : [A, ...Fill<R, N, Start, End, [...C, 0]>]
    : T

type R = Fill<[1, 2, 3, 4, 5, 6, 7], true, 0,1>;

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

type cases = [
  Expect<Equal<Fill<[], 0>, []>>,
  Expect<Equal<Fill<[], 0, 0, 3>, []>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 0, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0, 2, 2>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], 0>, [0, 0, 0]>>,
  Expect<Equal<Fill<[1, 2, 3], true>, [true, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 1>, [true, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 1, 3>, [1, true, true]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 0>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 10, 20>, [1, 2, 3]>>,
  Expect<Equal<Fill<[1, 2, 3], true, 0, 10>, [true, true, true]>>,
]