Nice hksong!

Actually, in real Pokemon, effectiveness is not always mirrored. In fact, even hitting the same type is not always guaranteed to be "not very effective".

Your solution only works for this kata. That is perfectly fine since that is the goal of code wars. What is not fine is to make false claims about things outside of code wars.

PS: If we were to follow the specifications of the kata exactly, all you would need is key value pairs of the super effective relationship. You can derive the not very effective relationships from that as well as from the fact that same types are always not very effective. Anything left over would fall under neutral. So your solution is not even optimized for this kata.

You should return the number once you have calculated it, that is all :).