I'll disagree that these questions require weeks of preparation. I think it's more just unfair because they favor a certain type of person: those whose interests align more strongly with the theory and algorithms and less with building things.

Of course, the irony is that for vast majority of the people they hire, most of the work they do will be building and not much algorithms work. So then what will happen is either you have people who are great at building things and force them to suffer through the interviews or you have people who are great at algorithms but not that interested in programming.

Of course, you might also have people who are great at both, but I wonder how many of them there are..