I applied for the position and quickly received a response that they were interested (about 1 day).

They informed me that there was first a technical interview, and if I passed that, they would schedule a second culture/fit interview.

Facebook provided access to a sponsored interview prep session by Gayle McDowell (author of "Cracking the Coding Interview"), which was offered on a twice-a-week basis indefinitely, in both in-person and online formats.

From this point on, it was clear that they were very interested in processing interview candidates at a rapid pace.

I scheduled my interview a week after their contact and ran prep (LeetCode.com offers many questions in the style of their whiteboard tech interview) as much as I could.

There were three other candidates in the lobby at the same time as me. I can only assume that they conduct as many as a couple dozen interviews daily at this rate (they were scheduled 15 minutes before me).

The technical interview is scheduled for a pretty tight 45 minutes (not hard, but they will stop you). You will be asked some sort of non-linear algorithmic question, and you MUST FOLLOW THE INTERVIEW PREP INSTRUCTIONS PRECISELY.

One of the options for outlining your solution is to perhaps include some pseudocode explaining your algorithm. I did this a little while trying to explain and was dinged for "jumped to coding right away."

As far as I can tell, they go through enough candidates that they can be extremely picky with their technical selection. Ace it, and you're golden. One misstep, and you're chopped liver.

Given an n*n matrix filled randomly with different colors (no limit on what the colors are), add up the total number of groups of each color. A group is adjacent cells of the same color touching each other.

Clarifying question: are diagonals adjacent? (A: no)