00298-medium-length-of-string

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type StringToCharacterArray<S extends string> =
  S extends `${infer Char}${infer Rest}`
    ? [Char, ...StringToCharacterArray<Rest>]
    : [];
    
type LengthOfString<S extends string> = StringToCharacterArray<S>['length']

Solution by Barrenboat #37277 

type StringToArray<S extends string, Arr extends string[] = []> = 
  S extends `${infer First}${infer Tail}`
  ? StringToArray<Tail, [...Arr, First]>
  : Arr;

type LengthOfString<S extends string> = StringToArray<S>['length'];

数组可以读取 Arr['length'] 属性，将字符串转换为数组

Solution by djdidi #37158 

type LengthOfString<S extends string, Count extends any[] = []> = S extends `${infer F}${infer R}` ? LengthOfString<R, [...Count, any]> : Count['length']

Solution by 359Steve #37059 

// your answers
type LengthOfString<S extends string, Res extends any[] = []> = S extends '' ? Res['length'] extends 0 ? 0 : Res['length']
  : S extends `${infer F}${infer L}` ? LengthOfString<L, [...Res, F]> : never;

Solution by AlexBraunMagic #36930 

type LengthOfString<S extends string, ARR extends string[] = []> = S extends `${infer F}${infer L}` ? LengthOfString<L, [...ARR, F]> : ARR['length']

Solution by tungulin #36747

type LengthOfString<S extends string, A extends any[] = []> = S extends ${infer _}${infer Rest} ? LengthOfString<Rest, [any, ...A]> : A['length'];

Solution by asylbekduldiev #36636 

// your answers
type LengthOfString<
  S extends string,
  A extends unknown[] = []
> = S extends `${infer _}${infer R}`
  ? LengthOfString<R, [...A, unknown]>
  : A['length']

Solution by goddnsgit #36183 

type Push<T extends unknown[], V> = [...T, V]

type LengthOfString<S extends string, TRes extends number[] = []> = S extends `${any}${infer Other}` 
? LengthOfString<Other, Push<TRes, TRes['length']>>
: TRes['length']

Solution by rize-the-flag #35996 

export type LengthOfString<S extends string, T extends Array<unknown> = []> = S extends `${infer _}${infer Rest}`
  ? LengthOfString<Rest, [...T, unknown]>
  : T['length'];

Solution by gangnamssal #35860 

type LengthOfString<S extends string,Acc extends any[] = []> = 
 S extends `${infer Start}${infer Rest}` 
 ? LengthOfString<Rest,[...Acc,Start]>
 : Acc['length']

Solution by EvilEl #35856 

type LengthOfString<S extends string, T extends unknown[] = []> = 
  S extends `${infer _}${infer Rest}` 
    ? LengthOfString<Rest, [unknown, ...T]> 
    : T['length'];

Solution by gangnamssal #35579 

type LengthOfString<
  S extends string,
  T extends string[] = []
> = S extends `${infer F}${infer L}`
  ? LengthOfString<L, [...T, F]>
  : T['length'];

Solution by RanungPark #35517 

// your answers
type LengthOfString<T extends string> = T extends `${infer first}${infer pending}`
    ? LengthOfString<pending>
    : never;

Solution by Sathiyapramod #35503 

// your answers
type LengthOfString<T extends string> = T extends `${infer first}${infer pending}`
    ? LengthOfString<pending>
    : never;

Solution by Sathiyapramod #35457 

type LengthOfString<S extends string, AsArray extends string[] = ['']> = S extends `${infer First}${infer Rest}` 
  ? LengthOfString<Rest, [...AsArray, First]>
  : { [K in keyof AsArray]: K extends `${infer Index extends number}` ? Index : never } extends [...unknown[], infer Last]
      ? Last
      : never

Solution by stackoverfloweth #35258 

type LengthOfString<S extends string, ACC extends string[] = []> = S extends `${string}${infer Rest}` ? LengthOfString<Rest, [...ACC, string]> : ACC['length']

Solution by eunsukimme #35229 

// 여기 풀이를 입력하세요
type LengthOfString<
  S extends string,
  T extends string[] = []
> = S extends `${infer F}${infer R}`
  ? LengthOfString<R, [...T, F]>
  : T['length'];

Solution by LeeKangHyun #35012

Use recursive type to make a split array. Then return its length.

// your answers

type SplittedArray<S extends string> = S extends `${S[0]}${infer Rest}` ? [S[0], ...SplittedArray<Rest>] : [];
type LengthOfString<S extends string> = SplittedArray<S>['length'];

Solution by dev-jaemin #35008 

// 你的答案

type StringToTuple<S extends string> = S extends `${infer A}${infer Rest}`
  ? [A, ...StringToTuple<Rest>]
  : [];

type LengthOfString<S extends string> = StringToTuple<S>["length"];

kill two birds with one stone.

Solution by shx123qwe #34966 

type LengthOfString<
  S extends string,
  T extends string[] = []
> = S extends `${infer F}${infer R}`
  ? LengthOfString<R, [...T, F]>
  : T['length'];

Solution by devshinthant #34581 

type StringToArr<S extends string> = S extends `${infer p}${infer rest}` ? [p, ...StringToArr<rest>] : []
type LengthOfString<S extends string> = StringToArr<S>['length']

Solution by ouzexi #34011 

type LengthOfString<S extends string, N extends any[] = []> = S extends ''
  ? N['length']
  : S extends `${infer A}${infer Rest}`
    ? LengthOfString<Rest, [...N, A]>
    : N['length']

Solution by laplace1009 #33805

type Len<T extends string, L extends string[] = []> = T extends ${infer K}${infer P}? Len<P, [...L, K]> :L["length"]

Solution by rookiewxy #33733 

type StringToArray<S extends string> = S extends `${infer a}${infer b}` ? [a, ...StringToArray<b>] : []
type LengthOfString<S extends string> = StringToArray<S>["length"]

Solution by mosey-san #33727 

// 先转个数组类型
type stringToArray<S extends string> = S extends `${infer F}${infer Rest}`
  ? [F, ...stringToArray<Rest>]
  : [];

type LengthOfString<S extends string> = S extends ""
  ? 0
  : stringToArray<S>["length"];

Solution by fyuanz #33686 

// your answers

type LengthOfString<S extends string, Result extends string[] = []> = S extends `${infer F}${infer R}`
  ? LengthOfString<R, [...Result, F]>
  : Result['length']

Solution by KeithChou #33219 

type LengthOfString<S extends string, L extends string[] = []> = S extends `${infer F}${infer Last}` ? LengthOfString<Last, [...L, F]> : L['length']

Solution by ZhipengYang0605 #32822 

type StringLength<T extends string, Acc extends 0[] = []> = T extends `${string}${infer Rest}`
    ? StringLength<Rest, [...Acc, 0]>
    : Acc['length']

Solution by ZhulinskiiDanil #32684 

type StringToTuple<S extends string> = S extends `${infer F}${infer Rest}`
  ? [F,...StringToTuple<Rest>] : []
type LengthOfString<S extends string> = StringToTuple<S>["length"]

Solution by avidang #32530 

type LengthOfString<S extends string, A extends string[] = []> = 
  S extends `${infer F}${infer R}` 
    ? LengthOfString<R, [...A, F]>
    : A['length']
  1. 스트링은 S['length'] 로 number까지밖에 타입 추론이 안된다.
  2. length를 정확한 숫자로 타입추론하기 위해서 배열에 스트링을 쪼개서 넣을 생각을 해야한다.

Solution by dev-hobin #32402