At the beginning, they conducted a phone interview. They explained the job to me, and I talked about myself.

Then there were four interviews, one hour each, spread over two days. If I passed the first two interviews, I continued to the other two.

All of the interviews were technical, with medium LeetCode-style questions.

Implement an iterator for a binary search tree. This means that every time the user calls the next function, it will return the next element until it returns NULL, if the user iterates through all the tree.