I was contacted by a recruiter who proposed a job offer to me, so I applied. After 3 days, we arranged a telephone interview that lasted 30-40 minutes.

First, the interview focused on past projects I worked on and the technical solutions I created to solve problems within those projects.

Then, we moved on to a technical interview covering manual memory management (retain, release, everything before ARC...), Grand Central Dispatch, and queue management. They also asked questions about memory allocation (stack, heap, and so on).

After a week, we arranged an "on-site" interview in London, at Finsbury Square. There were two interviewers, and the interview lasted for 2.5 hours.

This involved many "exercises," such as writing algorithms on paper (e.g., Fibonacci, quicksort, etc.). They also asked a lot of questions on "standard C" (this is the step where I probably failed).

Explain the differences between KVO and NSNotificationCenter.

If NSNotificationCenter didn't exist, how would you implement it?