Text was rewritten by moderator, so it became clearlier, I think

Translation approved

Thanks, fixed

Fixed, thanks

I realized that my first solution is not good and had some mistakes, so i brought not mine solution but valid one.

Ok, i think i'll do 50 cases of valid and 50 cases of invalid molecules.

Yes, I tried to do kata with 10 atoms H, F, Cl, Br, O, S, Se, N, P, C and others and ... i couldnt solve it :) Maybe it can be a series of katas starting from 7 and ending to 4-3 kyu with the growing complexity.

Random tests added, but need to check if they are OK

Thanks, fixed!

It doesn't work with punctuation marks!