Agree. I like your solution way more! tryed to use reduce at first, but didnt figured out, because forgot about Right version.

While you are correct in pointing out that big O notation ignores multiplication by a constant, in many real life situtations halving runtime is a significant change.

See my comment when somebody complained it's O(n^2). Btw, O(2n) = O(n).

What is readable is also a matter of experience and taste. For instance, some believe writing "u" instead of "you" is better readable, others don't think so.