I applied through another source. The process took four weeks.

I was shortlisted through HackerEarth. Once selected, I had to appear for the onsite hackathon. They booked the flight and provided a very great facility to stay.

• Part one: They checked my problem-solving ability by providing pen and paper and asking to implement code. I had to come up with the algorithm or logic in less than 45 minutes, otherwise I would get rejected, and I also had to share the implemented code on the Slack channel within an hour, including the 45 minutes.
• Final hackathon: Once I cleared the first round, there was a final hackathon in which I had to implement rotating cube logic, which had a duration of about one and a half days.

The HackerEarth questions included three graph questions that were variations of BFS, DFS, and Dijkstra's algorithm. There was one answer.

The first problem was to lock and unlock a node of the given tree. The structure of the tree had one root and multiple children, which was greater than two. The problem was to find a solution for locking and unlocking the nodes logic with log(N) complexity. Lock(node) returns a boolean. We can lock the node if and only if ancestor nodes and descendant nodes are not locked. If they are locked, then it returns false. Else, it returns true. Unlock(node) returns a boolean. If the node is already locked, then unlock it and return true. Else, return false. There were two answers.

The second problem was a rotating cube question that you will find on search.

The technical interview covered synchronization of threads, a distributed system to provide service to one point, and the difference between HTTPS and HTTP.