I really liked everyone I met with. You can see they not only hire people with technical skills, but they also hire positive people with good communication skills. The first interview was a well-designed, well-thought-out interactive whiteboarding session, a combination of algorithms as well as design. It wasn't difficult per se, but it was designed to test coding aptitude, design skills, and the ability to work in teams. They stressed SOLID principles in design. It was enjoyable.

The second interview was lunch.

The third was a design interview, focusing on UI plus architecture.

The fourth was another design interview, which touched upon architecture, design patterns, dependency injection, and testing.

The fifth was a LeetCode medium question.

The final interview was behavioral and business-oriented. It also touched upon architecture-related tech experience. There were no gotchas.

Can't say, but the usual trees and other data structures are important to know. Practice LeetCode questions, easy and medium.