A large employer in my past used to apparently conduct just this sort of "interview". I learned to my disgust a few years later that the division conducting th

A large employer in my past used to apparently conduct just this sort of "interview". I learned to my disgust a few years later that the division conducting those "interviews" were doing what they called a "brain suck". That is, they never intended to hire anyone, they were just using the unlucky "interviewees" to help them solve a software engineering problem for free.