Apple Software Engineer (Ios Developer) interview questions

I applied online for an iOS Engineer position. I was kindly contacted by the Apple recruitment team and we arranged a screen call with the technical manager of the team I applied for. The recruitment process use to take a couple of 30 min screen calls and a 1:1 interview. I didn't pass the first call. During the call I was asked about performance optimization, debugging, threading and algorithmic complexity of a suggested problem.

phone interview for 25 minutes. Started with a question about my background, then followed with technical questions about stuff in my resume. Had another phone interview interview with 3 other engineering managers, they were very technical (programming, software engineering, ..etc). Was invited for an onsite, got offer.