Yes!

Prefer this to the single line solutions, much easier to read :)

\w also ignores ö,ä,ß. It only matches [A-Za-z0-9_]

Pretty clean, without having to resort to regex dark wizardry. However, seems to dodge the problem's intent.

Without them I can put a '.' at the begining or end

😡

So neat. Next time I will string multiple conditions together. Thanks for sharing!

"efficiency" is generally related to time complexity, not space. ;) (but I have some extra layers there too, yes)

А very concise but inefficient solution due to high space complexity

+1 for readability and best practice, but this answer violates the specified constraints, which were implied by the message "answer goes here" placed between a single pair of slashes.

This is so clean. Please consider to add comments I really would like to understand how it works and the logic behind.