2059 - Drop String (🎥 Video Explanation and Solution)

[dimitropoulos]

2059 - Drop String

We've already done a similar challenge, DropChar which will drop a specific sequence of characters. This one is a bit more complex because it will drop any individual character in the provided pattern. Loops within loops. Turtles all the way down.

🎥 Video Explanation

🔢 Code

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

type A1 = DropString<'butter fly!', ''>;
type B1 = 'butter fly!';
type C1 = Expect<Equal<A1, B1>>;

type A2 = DropString<'butter fly!', ' '>;
type B2 = 'butterfly!';
type C2 = Expect<Equal<A2, B2>>;

type A3 = DropString<'butter fly!', 'but'>;
type B3 = 'er fly!';
type C3 = Expect<Equal<A3, B3>>;

type A4 = DropString<' b u t t e r f l y ! ', 'but'>;
type B4 = '     e r f l y ! ';
type C4 = Expect<Equal<A4, B4>>;

type A5 = DropString<'    butter fly!        ', ' '>;
type B5 = 'butterfly!';
type C5 = Expect<Equal<A5, B5>>;

type A6 = DropString<' b u t t e r f l y ! ', ' '>;
type B6 = 'butterfly!';
type C6 = Expect<Equal<A6, B6>>;

type A7 = DropString<' b u t t e r f l y ! ', 'but'>;
type B7 = '     e r f l y ! ';
type C7 = Expect<Equal<A7, B7>>;

type A8 = DropString<' b u t t e r f l y ! ', 'tub'>;
type B8 = '     e r f l y ! ';
type C8 = Expect<Equal<A8, B8>>;

type A9 = DropString<' b u t t e r f l y ! ', 'b'>;
type B9 = '  u t t e r f l y ! ';
type C9 = Expect<Equal<A9, B9>>;

type A10 = DropString<' b u t t e r f l y ! ', 't'>;
type B10 = ' b u   e r f l y ! ';
type C10 = Expect<Equal<A10, B10>>;

// ============= Your Code Here =============
type DropString<T, U> =
  T extends `${infer Head}${infer Tail}`
  ? U extends `${string}${Head}${string}`
    ? DropString<Tail, U>
    : `${Head}${DropString<Tail, U>}`
  : '';

// ============== Alternatives ==============
type DropChar<T, U extends string> =
  T extends `${infer Left}${U}${infer Right}`
    ? DropChar<`${Left}${Right}`, U>
    : T;

type DropString<T, U> =
  U extends `${infer Head}${infer Tail}`
  ? DropString<DropChar<T, Head>, Tail>
  : T;

➕ More Solutions

For more video solutions to other challenges: see the umbrella list! #21338