I had an on-campus interview with Facebook at my university, which was one-on-one and lasted about 45 minutes.

In this first interview, I was given three binary search tree questions to answer.

A few weeks later, I had another interview on Facebook's campus in Menlo Park. Afterward, I got to tour the entire place with a group of other intern candidates.

That second interview was also about 45 minutes and focused on a single question about sorting arrays efficiently.

Some of the other intern interviewees had two questions, but I focused on solving the one problem well. I came up with a few solutions and wrote out the code in C++ for the most efficient one.

It was a very cool campus with very cool people!

Sort an array of characters into three groups, in O(n) time and using little extra memory.