I like that recursion! very clever!!

Here is our hero

The inner ''.join is necessary because sorted returns a list not a string, so you can't concatenate the two outer strings with the inner unless it is joined first.

sum of arithmetic progression

That little engineer part at the end was a great hint.

also the "".join is unnecessary

can you pls explain why yours works

or in a return statement. Wow

Should not be forked from here as it is not about being smart (and smarter) with Python complex numbers.

I tried to exploit the life attribute of the object and it worked for the practice cases. How did you remove it for the tests

I wrote my openion. This code is elegant

O(n * log(n)) when it can be done in O(n). This is not best at all.

Best I think

made it a lot shorter though the speed is similar due to the fact that yours inserts the value which is slower

oh, when talking about byte-count, you where talking about the number of chars. 'Thought you were talking about the bytecode, actually. x)