the code you pasted passes the tests as of now, so we cannot replicate the issue

Yeah, superb that someone made a benchmark on this :) I would say that the results confirm the idea that just simply filling in the 1-s "in a spiral" should be faster than doing some more complex operations with lists etc. (as can be seen in some other solutions). Moreover, for me, this solution is maybe the most readable / comprehensible... :)