Yes, I think the instructions should be more specific and tell people the format of possible inputs. Is empty array or None or [None] or [None, None] possible input? How to treat None? Ignore it or count it as a placehoder and treat it as 0? I can't figure out what's wrong with my code. I only got very short error message which just caused more confusion rather than being helpful! :(

Resolved until further notice.

Thanks. I've edited the description to include the points you mention.

Thank you for valuable feedback. I have implemented your suggestion. The description was weird but it kind of grew over time as I got more feedback from people. Thanks again.