02059-hard-drop-string.ts

// ============= Test Cases =============
import type { Equal, Expect } from './test-utils'

type cases = [
  Expect<Equal<DropString<'butter fly!', ''>, 'butter fly!'>>,
  Expect<Equal<DropString<'butter fly!', ' '>, 'butterfly!'>>,
  Expect<Equal<DropString<'butter fly!', 'but'>, 'er fly!'>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', 'but'>, '     e r f l y ! '>>,
  Expect<Equal<DropString<'    butter fly!        ', ' '>, 'butterfly!'>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', ' '>, 'butterfly!'>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', 'but'>, '     e r f l y ! '>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', 'tub'>, '     e r f l y ! '>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', 'b'>, '  u t t e r f l y ! '>>,
  Expect<Equal<DropString<' b u t t e r f l y ! ', 't'>, ' b u   e r f l y ! '>>,
]


// ============= Your Code Here =============

type StringToUnion<T extends string> = T extends `${infer First}${infer Rest}` ?
  First | StringToUnion<Rest>
  :
  T

type Test1 = StringToUnion<'Hello'>

type DropString<S extends string, R extends string, T = StringToUnion<R>> = S extends `${infer First}${infer Rest}`
  ? First extends T
    ? DropString<Rest, R>
    : `${First}${DropString<Rest, R>}`
  : S

type Test2 = DropString<'butter fly', 'but'>