9896 - GetMiddleElement (Fast & Slow Pointers)

[idebbarh]

type Shift<T> = T extends [any, ...infer Rest] ? Rest : never;

type GetMiddle<T extends unknown[], K extends unknown[]> = T extends [
  infer First,
  infer Second,
  ...any
]
  ? K["length"] extends 0
    ? [First, Second]
    : [First]
  : T;

type GetMiddleElement<
  T extends unknown[],
  Fast extends unknown[] = T,
  Slow extends unknown[] = T
> = Fast extends [any, any, ...infer Rest]
  ? GetMiddleElement<T, Rest, [] extends Rest ? Slow : Shift<Slow>>
  : GetMiddle<Slow, Fast>;