The interview is basically designed to see if you can match the same kind of cleverness as your interviewer. The questions are completely academic in nature and do not reflect real-world software development in practice.

They use a code-sharing tool live that doesn't allow you to execute or debug the software, despite the tools they refer you to in order to prepare having them.

At the end, my interviewer of 7 years with the company gave me a perfect quote. He said when he was interviewing, he had to run through over 200 practice examples before he interviewed.

This alone demonstrates how Facebook's interview process is not designed to test practical scenarios or a developer's innate abilities.

I had to solve a problem in an exact, specific way and was forced to use recursion. This was despite memory use being a stated concern. Recursion should rarely be used in reality due to the risk of stack overflows, a higher risk of bugs, and the likelihood of lower performance due to increased cache misses.