Hi all, thank you for the help! I just got it. Thanks especially to Stryder_ZX25 which pointed out the flaw in my solution (the stack overflow link was exactly what I needed). It was a sutil thing that I would not have paid attention to otherwise.

To be honest I don't know either that's why I suggested "trying" withoput pointing out a potential "mistake/useless operation" (I have tried the same thing and it times out compared to the += approach and the two solutions have 8 secs difference between them). I have tried to time both approaches on my local machine and it seems to be minor. Theoretically, I don't think there is a difference because strings are immutable and both approaches should create a new string (as far as I understand). I am looking through the cpython github and if I find something I will update the thread.

Update: I have tried OP's solution as is and it timed out. I have tried the inplace addition and reversing and it worked. I have also tried appending (without inplacing) but at the end and not the beginning then reversing and it also worked. So that seems to be what makes a difference. I am not sure how strings are implemented in python (probably linked lists or something similar) but once I can find the source code for (which I couldn't find, can't find a "_string" file on the github repo) I will update my reply.

Update 2: Check this stack overflow thread : https://stackoverflow.com/questions/37133547/time-complexity-of-string-concatenation-in-python. In the accepted answer's footnote there is a mention of an optimisation to string concatenation. In short when you define two string strA and strB, cpython will avoid creating a new copy when using strA = strA + strB or strA+=strB but not when using strA = strB + strA (prepending). This is in line with what I found so I think it is correct. I hope This helps. Take it with a grain of salt though.

If anyone has a better answer or explanation, then please correct me and/or append to the thread.

The JavaScript translation needs a test for the edge case when all arguments are '0'.

Thanks @Chrono79 - I never thought about checking that way.

It seems original kata author is inactive, so I guess it's up to you @Sigmanificient to decide?

I haven't solved in any other languages so I don't know if there's a similar "solution" available in those.

https://www.codewars.com/kata/5324945e2ece5e1f32000370/revisions You can see direct edits there, it was @Sigmanificient

Please don't use Issue tag for problems with your code - it is reserved for serious problems with the kata itself.

Your current code doesn't work and you need to debug - for example, try your approach on the inputs '1' + '10' -> your current solution gives '20' as the answer instead of '11'.

@livxy seems like you got your wish answered a few days later O_o

But who did the Python translation? I don't see any posts in the Discourse? Because they/author has to decide if they want to allow this solution:

https://www.codewars.com/kata/reviews/63667b68a16feb00010987d0/groups/636686f0dee82c0001a31bf5

(I thought it was cool personally, but this already is a pretty generous 4 kyu so...)

I will not be able to say more precisely.If you will realise it right, you would find solution not so hard. But without seeing your option I can't be more specific. May be only "try to use step debuging" )