import { factorial } from "https://deno.land/x/30_seconds_of_typescript@v1.0.1/util.ts";
Calculates the factorial of a number.
Use recursion.
If n
is less than or equal to 1
, return 1
.
Otherwise, return the product of n
and the factorial of n - 1
.
Throws an exception if n
is a negative number.