Wait... that interview question feels like it has quite a few traps set up in it...

The point of that question wasn't to do something silly like write some wrapper class for the array where get and set are redefined to index the array in a rotated way, right? Also, for square matrices, you can do both operations in place with constant memory overhead, was that what they were looking for?

And if you ask if it's an array of arrays, their complaint might be about the fact that 2d arrays are just 1-D arrays indexed differently and not actually jagged arrays, unless you're in in language like C#, where jagged arrays are better for some reason I don't remember. But unless you're doing a lot of numerical stuff or data science, there's no point in knowing that...