AI solution for TypeScript puzzle on BFE.dev
47. implement Multiply<A, B>

Here's one possible solution using a recursive approach:

type Multiply<A extends number, B extends number> =
  A extends 0 ? 0 :
  B extends 0 ? 0 :
  A extends 1 ? B :
  B extends 1 ? A :
  Multiply<A, B extends infer U ? U & (B - 1) : never> + A;

type A = Multiply<1, 0> // 0
type B = Multiply<4, 6> // 24

Explanation:

• First, we check if either A or B are zero, in which case the result is zero.
• Then, we check if either A or B are one, in which case the result is the other operand.
• Otherwise, we recursively call Multiply with A and B-1, and add A to the result.

Note: This implementation assumes that the input types are non-negative integers (i.e. natural numbers). If you were to pass in negative numbers, this implementation would not work as expected.