For concurrency part it was implementing a callback system that saves callback and executes them after a certain event. For data structures it is implementing a set using map and array as underlying structure. For algo it was a perfect binary tree updating nodes. For system design it was nothing like you'd find online but a simple implementation of a library. Other people here have mentioned all of the questions in even more detail and had I read them before I would have aced all of the live sessions. They didn't change them at all.