gtkatakura · October 6, 2022 04:21 · Apr 20, 2022 · Apr 20, 2022
diff --git a/fizzbuzz.ts b/fizzbuzz.ts
@@ -0,0 +1,110 @@
+
+
+
+type Reverse<A> =
+  `${A}` extends `${infer AH}${infer AT}`
+    ? `${Reverse<AT>}${AH}` : A
+
+type Digs = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+type DigsNext<I = Digs, R = {}> =
+  I extends [infer Head, infer Next, ...infer Tail]
+    ? DigsNext<[Next, ...Tail], R & Record<Head, Next>>
+    : { [K in keyof R]: R[K] }
+type DigsPrev = { [K in keyof DigsNext as DigsNext[K]]: K }
+
+type AddOne<A> =
+  A extends `${infer AH}${infer AT}`
+    ? AH extends '9' ? `0${AddOne<AT>}` : `${DigsNext[AH]}${AT}`
+    : `1`
+type SubOne<A> =
+  A extends `${infer AH}${infer AT}`
+    ? AH extends '0' ? `9${SubOne<AT>}` : `${DigsPrev[AH]}${AT}`
+    : never
+type Add<A, B> =
+  A extends `${infer AH}${infer AT}` ?
+    B extends `${infer BH}${infer BT}`
+      ? BH extends '0' ? `${AH}${Add<AT, BT>}` : Add<AddOne<A>, SubOne<B>>
+      : A : B
+type Mul<A, B, R = '0'> =
+  A extends '0' ? R :
+    B extends '0' ? R :
+      A extends `${infer AH}${infer AT}`
+        ? AH extends '0' ? Mul<AT, `0${B}`, R> : Mul<SubOne<A>, B, Add<R, B>>
+        : R
+type Multiply<A extends string | number | bigint, B extends string | number | bigint> =
+  Reverse<Mul<Reverse<A>, Reverse<B>>>
+
+
+type Division<
+  W extends number,
+  D extends number,
+  Error extends any = never,
+  Q extends string = '0'
+  > =
+   W extends 0
+      ? Q extends never ? Error : Q
+      : W extends never ? Error : Division<Subtract<W, D>, D, Error, AddOne<Q>>
+
+type ConstructTuple<
+  L extends number,
+  R extends unknown[] = []
+  > = R["length"] extends L
+  ? R
+  : ConstructTuple<L, [...R, unknown]>
+
+type Subtract<
+  M extends number,
+  S extends number
+  > = ConstructTuple<M> extends [...subtrahend: ConstructTuple<S>, ...rest: infer Rest]
+  ? Rest["length"]
+  : never
+const div: Division<9, 3> = "3"
+const div: Division<15, 3> = "5"
+
+type FizzBuzzValidator<
+  V extends number
+  > =
+  Division<V, 3> extends never
+    ? never
+    : Division<V, 5> extends never
+      ? never
+      : 'FizzBuzz'
+
+type BuzzValidator<
+  V extends number
+  > =
+  Division<V, 3> extends never
+    ? never
+    : 'Buzz'
+
+type FizzValidator<
+  V extends number
+  > =
+  Division<V, 5> extends never
+    ? never
+    : 'Fizz'
+
+type FizzBuzz
+  <V extends number> =
+  FizzBuzzValidator<V> extends never
+    ? FizzValidator<V> extends never
+      ? BuzzValidator<V> extends never
+        ? V
+        :'Buzz'
+      :'Fizz'
+    :'FizzBuzz'
+
+const res: FizzBuzz<2> // 2
+const buzz: FizzBuzz<3> // Buzz
+const fizz: FizzBuzz<5> // Fizz
+const fizzBuzz: FizzBuzz<15> // FizzBuzz
+
+type FizzBuzzArr<
+  V extends Array<number>,
+  A extends Array<any> = []
+  > =
+  V extends [infer E, ...infer D]
+    ? FizzBuzzArr<D, [...A,  ...[FizzBuzz<E>]]>
+    : A
+
+const FIZZBUZZZZ: FizzBuzzArr<[1,2,3,4,5,6,7,8,9, 15]> //  [1, 2, "Buzz", 4, "Fizz", "Buzz", 7, 8, "Buzz", "FizzBuzz"]
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