Similar to others, I first received a LinkedIn message from a Facebook HR staff member based in India.

We scheduled the first phone interview, which was a simple quiz with five multiple-choice questions, conducted by the HR staff.

Afterwards, I had the second and third interviews with Facebook iOS engineers. These were with different people, but the format was pretty much the same.

Each interview was about 45 minutes to 1 hour and involved live coding on coderpad.io.

I progressed, and Facebook flew me from Sydney to Silicon Valley for a face-to-face interview. It lasted from 10 AM to 3 PM and touched on many areas, including:

• Behavioral questions
• iOS app architecture
• Writing code on a whiteboard
• Time and space complexity

I did not receive an offer in the end but was very impressed by the process.

Given a number (e.g., 234), print all combinations of its dial pad letters (e.g., "adg", "adh", "adi", "aeg", "aeh", "aei", ...).