I called them out on this in one of the Who's Hiring posts they always comment on. This seems like a reallllyyyy obvious problem for them...
Which culminated in this blog post: https://news.ycombinator.com/item?id=3061860
Call me weird, but I prefer the assignments than the mindless discussions about balancing trees and Big-Oh notation.
A well designed take home assignment, meanwhile can be a good filter, telling you immediately if the candidate knows the basics and has the added benefit of showing you strengths and weaknesses in their practice.