I applied online and also with a recruiter. This was the standard process: I set up a phone screening a couple of weeks out.

The interviewer was definitely not the one listed in the email (possibly a last-minute replacement). He must have been sitting in an open area at first; I had to mention the heavy background noise twice (I could hear voices, though not exact words, before he made his first adjustment).

Because of the level I was asked a lot of platform (iOS) questions, primarily around threading, in a rapid-fire manner. I know I did well on the algorithms (I saw a more complicated version of one of them before) and even had time at the end to discuss, but not code, a variant on one question. However, I supposedly did not answer the platform/threading questions fast enough, so the hiring committee (for a phone screen) declined to invite me for an onsite. Very likely I would not have moved on regardless of the background noise, but it didn't help.

Strong vs. Weak?

What will happen if you dereference a block?

Talk about threading. What are the pros and cons of each method?

Describe dispatch sync vs. async. When should you use sync?

What are the parameters of dispatch_queue?

Are parallel and concurrent the same or different?

Main thread vs. main queue?

Valid parentheses with other characters, e.g., (()e45).

NestedInteger weight sum: Given a class with callable methods isInteger, getInteger, and getList, get the weighted sum. For example, {1,{4,{6}}} results in 1 + (4*2) + (6*3) = 27.