It's an attempt to understand how you would solve problems of the class that the question is of, not an attempt to get a solution to a specific problem.
Not using a library when you should have is a problem solved by a 20 second code review.
Code reviews are normally done after the developer has spent some time on the code. That is fine that it takes 20 second to determine the code is totally worthless, but the developer has already wasted DAYS of effort.
Not using a library when you should have is a problem solved by a 20 second code review.