I completed OA for Airbnb.

There were 4 levels and you have to complete the code in method structures based on requirement.
The next level has higher difficulty than prev.

The questions were lengthy but was really simple. I am able to complete 2 levels and 3rd level half-way.

Learnings:

1. Read requirements carefully
2. I was stuck at 1 point for more than 20 mins - You can reuse above methods for current method impl.
3. Time is major factor over here
4. If test case not passing of current method - it may depend on for earlier already implemented methods for data
5. score showing 400/600