I think that it is not possible to change the level.

But this is a perfectly valid protocol for circular lists? One of a few possible, but still, a good one. It is also very clearly defined and well described.

Someone did totals.pop().

I hate to break it to you, but the "1665 of 6975 completions" thing means that 1665 users completed it out of all 6975 completions in your selected language (which appears to be JS). It's true though that g964 kata descriptions aren't great.

There is no such thing as 'O(2n)' in big O notation. There are different notations which keeps the constant multiplier before function, such as 'tilde notation', see https://www.reddit.com/r/compsci/comments/1bl0q8/tilde_notation/. But you are right this solution is quite inefficient.