A friend referred me to Facebook, and the hiring recruiter emailed me the next day. He asked for my resume, stating that he would send it to the hiring manager. The following day, the recruiter asked for convenient days and times for a call, and contacted me the day after that. He explained the hiring process, asked about myself, and what I did and currently do.

Then, a week later, I had a technical phone interview with a Facebook employee. We used Google Docs for the session. She first asked me a bit about myself and then posed one technical question. I had to write C/C++ code in Google Docs while explaining my thought process over the phone.

It was quite challenging. Not just the question itself, but the entire experience. You feel pressure if you make a typo (and I made many silly typos that I usually don't make when writing code) because she could see my typing in real-time. Additionally, I couldn't debug or use any tools.

In the end, to understand my proposed solution, she gave me an example input and asked me to traverse it using my code. After grasping my idea, she said, "Okay, almost correct. You could find a bug in 10 minutes, yes, but we need to wrap up now."

The next day, the original recruiter emailed me, informing me that they wouldn't be proceeding with my application. It seems they required a correct solution and code to be completed on the fly within 25 minutes.

Given a set of integers, print out all its subsets.

Write C/C++ code to solve it.