Read up on Glassdoor about the interview:
When applying through a recruiter:
- Basic screening test from a recruiter - basic programming questions that you really should know.
- Followed by two 1 hour Skype interviews, both interviews consisted of 1 programming question and then 15 mins chatting.
- The questions at this stage are very basic (arrays).
- Final stage was onsite interview, 4 back to back interviews, these were a lot harder but with good revision easily passed.
- Make sure you know your data structures and basic algorithms.
Facebook employee referral :
- 1 telephonic round
- 4 onsite (1 Cultural fit + 1 Design + 2 Coding)
- Most of the questions in the coding round were on algorithm fundamentals. Also they expect clean coding with proper testing
- The design round is more like the discussion you would have with your teammate suggesting pros and cons of each method.
- You should understand: Clean code, test cases, scalable design, high level design
So the best way to prepare for the Facebook interview is knowing/being able to do all of the above!