Apple Sr Software Engineer interview questions

The posting was for a skilled Objective-C engineer with experience developing SDKs and frameworks. Had a few phone interviews with the in-house recruiter and the hiring manager, these went well. I was scheduled to have a follow-up phone interview with one of the lead engineers, however an emergency conflict came up and he needed to reschedule. I was coincidentally scheduled to travel to Apple for an on-side interview with another group in a few days so we coopted the trip, splitting the interviews with the two groups over two days. This interview review is related to the first day/group only. I'll post a separate review for the second day/group later. The engineers, the manager, and the recruiter were all very friendly, easy to converse with. The knowledge-based programming questions were difficult but manageable -- several pertained to nonatomic/atomic properties, retain cycles, some bitwise operations, and delegates vs. blocks vs. notifications. The coding questions primarily related to data structures and optimization, with a little UI coding towards the end. By the end of the day I was exhausted and more than a little demoralized. I should've performed better. I had a few shining moments, but these were overshadowed by some glaring gaps in my memory on some of the early basics of data structures and algorithms. I left them with the impression that I was really more of a framework *consumer* than a competent framework *author*, and that I wasn't really ready for the challenges that this posting entails. Nevertheless, the engineers and the manager were stellar. They were friendly, not dismissive, and helpful particularly when I was flailing. I would've been honored to work with all of them.