The string only contains letters from a to z?

A string also has a length property. Don't need to convert the string to an array with split().

Sorry, wil do!

When no value is passed to reduce(), like ([]), where the initial value is 0. The reduce returns it's initial value.

What he is saying is that the function is mutating the original signature array.
You should make a copy of the signature array. You can do that with const aryintSignature_Copy = [...signature];

Wow, such a clever sollution!
I was breaking my head on excluding those 'edge cases' (n =< signature.length) from the loop.

What would be a good practice to eliminate overcomplification?
Is it to write all possible inputs and outputs in 1 overview to spot the most efficient pattern?

But thnx, this was a great lesson.

Oke, but what is returned when count_sheep(0) is executed? Not an empty ""...

But where is the logic for handling the '-' and ' ' at the first index and last index of each argument?