iOS interview questions reported at Walmart

2 questions candidates reported being asked at Walmart. Anonymous and unverified, so treat it as a hint of what to expect.

They cover Memory, ARC & runtime, Concurrency. Every question below links to a full answer with the common traps and the follow-ups an interviewer is likely to ask, so you can practise the way the interview goes: answer first, then defend it.

1. What is a retain cycle, and how do you find and fix one? 3.3.1
2. What is the difference between serial and concurrent queues and between sync and async, and what do QoS and target queues do? 10.1.1