[Typescript] 124. Binary to Decimal

Implement BinaryToDecimal<S> which takes an exact string type S consisting 0 and 1 and returns an exact number type corresponding with S when S is regarded as a binary. You can assume that the length of S is equal to or less than 8 and S is not empty.

type Res1 = BinaryToDecimal<'10'>; // expected to be 2
type Res2 = BinaryToDecimal<'0011'>; // expected to be 3

 

/* _____________ Your Code Here _____________ */
type NumberToArray<T extends number, R extends 1[] = []> = R['length'] extends T ? R : NumberToArray<T, [...R, 1]>;

type GetTwice<T extends unknown[]> = [...T, ...T];

type BinaryToDecimal<S extends string, Result extends unknown[] = []> = S extends `${infer First extends number}${infer RT}`
  ? BinaryToDecimal<RT, [...GetTwice<Result>, ...NumberToArray<First>]>
  : Result['length'];


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

type cases = [
  Expect<Equal<BinaryToDecimal<'10'>, 2>>,
  Expect<Equal<BinaryToDecimal<'0011'>, 3>>,
  Expect<Equal<BinaryToDecimal<'00000000'>, 0>>,
  Expect<Equal<BinaryToDecimal<'11111111'>, 255>>,
  Expect<Equal<BinaryToDecimal<'10101010'>, 170>>,
]