2257 - MinusOne

[Chen0x00]

type Digital = '0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'
type MakeDigitalArray<
  N extends Digital,
  T extends any[] = []
> = N extends `${T['length']}` ? T : MakeDigitalArray<N, [...T, 0]>
type Multiply10<T extends any[]> = [...T,...T,...T,...T,...T,...T,...T,...T,...T,...T]

type ToArray<
  S extends number|string,
  T extends any[] = []
> = `${S}` extends `${infer F}${infer L}`
      ? F extends Digital
        ? ToArray<L, [...Multiply10<T>, ...MakeDigitalArray<F>]>
        : never
      : T

type Minus<
  S extends number,
  N extends number
> = ToArray<S> extends [...ToArray<N>, ...infer L] ? L['length'] : 0

type MinusOne<S extends number> = Minus<S, 1>