Somebody tell me how he did that

You can use the pythagorean theorem.

Clever, but it shouldn't be best practice as it would count "garbage" as "good".

(And yes, I know the kata doesn't have such inputs, but that isn't the point..)

Clever, I like it :)

I meant that he made the regex filter unique cases just like a set :)

(I on the other hand used both which is slower..)

Why you want he put a set ? It's work properly like that. Add a set will affect performance.

thank you for your suggestion :) (mine looks same as him)

just retake a look on it.

Because you're probably using multiplication instead of division

bad ass

Cool one :)