I applied online for a few Firmware Engineer positions on the Apple website and was contacted by two different recruiters for two separate teams. I had a brief HR screen with both of them and then a further phone screen set up with both team's Hiring Managers. These interviews mostly involved in-depth questions about my resume and also some code exercises that I completed successfully.

I was informed the next day after both initial interviews that they would like to move forward. In both cases, I was told that a second technical phone screen would be set up with a member of the respective teams I was interviewing with.

This second round of phone interviews was also very technical, and I performed well in them. The recruiters for both teams then informed me that they would like to bring me to California for a day of interviewing.

Managing this was a bit disorienting, as each team's recruiter seemed to operate autonomously. Since flying cross-country would eat into my vacation time, I told them that I would like to interview with both teams on the same trip. In hindsight, this was a bad idea.

My first interview went terribly. It consisted of about eight interviews with one person each, back-to-back, lasting approximately 45 minutes to an hour each. The setting was a claustrophobic meeting room, the size of a literal closet, where we had to get out of each other's way to use the whiteboard.

At least two of the interviewers were openly contemptuous of my lack of experience in a particular technology. This technology was never mentioned on my resume, and I had explicitly asked during my phone screens whether this would be a problem, having been assured that it would not.

One interviewer even made a point of visibly making notes on my resume, such as "Does not know X," and making snide remarks about how he was surprised I "did not even know this."

I should really have stood up and walked out at this point, but I didn't. The day continued in this vein until the evening. At the end, I was sure that I would probably not get the offer and was almost sure that I would not have accepted even if they had extended one. I spent the evening fuming and had a bad night.

My second interview was the next day and was a whole different experience. The interview rooms were slightly less terrible in this building. There were four different interviews, lasting about an hour, with two interviewers together.

I got the distinct impression that they were trying to ascertain my skills and experience, as opposed to getting under my skin. Unfortunately, I was so frazzled and upset about the previous day that I missed a few questions that I really would have answered well in a better frame of mind. I am pretty convinced that if this had been the first interview I had had, my chances of getting an offer would have been much higher.

Write a function that, when given a certain set of numbers, displays all possible subsets of it.