I attended Facebook's University Day, where about 20 university students were present for interviews. The day started with the interview itself, followed by a five-hour tour of the Facebook campus and opportunities to learn more about the company.

When the interview process began, all of us were sitting in a room, and interviewers would come in to call our names. I watched as interviewer after interviewer entered with cheerful expressions and called out the names of other students. After about five minutes, my interviewer arrived and called me.

He was a heavy-set man, dressed sloppily, and had a look on his face as though he didn't want to be there. I could tell right away that the interview would not go well. When we entered the interview room, he immediately began asking technical questions. He didn't ask any questions about me to get to know me, whereas other students mentioned their interviews began with a discussion about their backgrounds.

Throughout the entire interview, I had the impression that my interviewer just wanted to rush me through so he could move on to something else. He asked me two questions: one went well, and with the second, I had some trouble.

My recruiter had told me beforehand that if we got stuck on a question, our interviewer would make an effort to get us back on track by offering hints. My interviewer did no such thing. I even explained what I was trying to do and why I was getting stuck, implying that I could use a hint. He just sat there without saying anything.

Finally, after I had spent about ten minutes trying different ways to solve the problem, he informed me that we were running out of time and hurried me through the rest of the problem. He gave me the last five minutes to ask him questions.

Given that I felt he was being forced to be there, one of my questions was whether Facebook employees have dedicated interviewers or if random employees are selected to interview candidates from time to time. He confirmed it was the latter. Therefore, I knew he was being forced to be there and just wanted it to end.

After the interview concluded, he walked me back to meet the other students. By this time, I already knew he wasn't going to give me a good review, but Facebook doesn't allow you to leave at this point. You are required to spend five hours learning about how wonderful it is to work at Facebook, highlighting all the good things you just missed out on.

A week later, I received my rejection email.

Given a binary tree, write a function that prints all paths from the root node to the leaf nodes.

What are the function's runtime and space requirements?

Given a linked list where each node's value can itself be a linked list (a recursive linked list), write a function that flattens it.