[bragh]

Because in many languages, this is trivial to the level of calling .reverse() on the array.

[walrus1066]

In which case, the question isn't really relevant to the job. Same goes for stuff like sorting algos. Why not pose problems more representative of the job and business domain?

[dragonwriter]

Sure, but in some of the popular languages where that is the case, .reverse() is no more (and no less) a “library feature” than creating or indexing an Array.