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 DropString<S extends string, R extends string> = R extends ''
  ? S
  : S extends `${infer Char}${infer Rest}`
  ? Include<R, Char> extends true
    ? DropString<Rest, R>
    : `${Char}${DropString<Rest, R>}`
  : S;
type Include<S extends string, R extends string> = S extends `${infer L}${R}${infer R}`
  ? true
  : false;
type Test = Include<'s', 's'>;
type Test2 = Include<'st', 's'>;