I followed up a week later and learned they had rejected me; apparently I wasn't focused on the problem (??), and I used the wrong data structures. D

I followed up a week later and learned they had rejected me; apparently I wasn't focused on the problem (??), and I used the wrong data structures. Damn. I'm sorry. To me this represents a very poor interview process. I just received two senior engineer job offers from companies with whom I actually ran into some roadblocks during the whiteboard/CoderPad sessions. Before the sessions, both companies stressed that the exercises were about my thought/communication processes more than the code itself. During the coding exercises I aced some things, and when I had some roadblocks I explained my thought processes and they nudged me in the right directions -- in both cases they were actually pretty fun and collaborative processes. That's really what they were testing for. Sounds like your interview was more like, "complete this fairly challenging coding assignment in silence while somebody looks over your shoulder," which is just not good interviewing. That's not a good simulation of an actual work environment. I had some total BS interviews too, at other companies. Some people/companies just suck at it.