IsOdd

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题目

return true is a number is odd

解答

type IsOdd<T extends number> = `${T}` extends `${number | ""}${
  | 1
  | 3
  | 5
  | 7
  | 9}`
  ? true
  : false;

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type Odd = 1 | 3 | 5 | 7 | 9;
type Last<T extends string> = T extends `${any}${infer S}${infer R}`
  ? Last<`${S}${R}`>
  : T;

type IsOdd<T extends number> = Last<`${T}`> extends `${Odd}` ? true : false;

// other way
// type Last<T extends string> = T extends `${any}${infer S}${infer R}` ? Last<`${S}${R}`> : T;

// type IsOdd<T extends number, \_SWITCH extends boolean = false, \_Counter extends 1[] = []> =
// `${_Counter[`length`]}` extends Last<`${T}`> ? \_SWITCH /_return_/ :
// IsOdd<T, \_SWITCH extends true ? false : true, [..._Counter, 1]>;

// simple way
// type IsOdd<T extends number> = `${T}` extends `${number}${1 | 3 | 5 | 7 | 9}` ? true : false;

simple way : #30334 (comment)