Are numbers starting with '0' are also consider valid, e.g.:
90 ---> 90 or 90 + 09

This Kata xD
It sounds easy at the beginning, but then number of exceptions to be taken into consideration is damn high.

Good job on preparing such Kata, there are not many problems (on Codewars) like this one.

I see it now, 100 random tests :)

I know this feeling bro :)
Do you know how many 120x120 tests are out there?

My current solution passes around 40-60. I want to know whether I should look for better algorithm or just optimize it?

Thanks ;)

Thanks, I got it now.
Not sure how I have not noticed it earlier.

In description you can read: 'String lengths are less than 5000'
The tests are extremly complex. There are a few tests with over 1000 signs length. Optimation is the main problem in this Kata. To be honest I am strugling as well.

This Kata is painful. My brain hurts!!

Thanks for answer

How many test cases are prepared for Python?

This seems to be much harder than 5 Kyu (current level) ;)
Probably ~ 3/4 Kyu would be suitable.

There is no need to write special cases. You should remember though about 'decode("utf-8")' and 'encode("utf-8")' methods.
UTF-8 is your friend and make sure that you make use of its help at every point.