4260 - AllCombinations

[justBadProgrammer]

// your answers
type Permutations<
    T extends string,
    A extends string=T>=
    [T] extends [never]
    ? ''
    : T extends string
    ? `${T}${Permutations<Exclude<A,T>>}`|Permutations<Exclude<A,T>>
    : never ; 

type StringToUnion<
    S extends string> = 
    S extends `${infer R}${infer U}`
    ? R|StringToUnion<U>
    : never ;

type AllCombinations<
    S extends string> =
    Permutations<StringToUnion<S>> ;