I went through four rounds of interviews, and almost all of them went quite well. Yet, the HR department never bothered to send a rejection email, even after two follow-ups.

This was a worst interview experience. The staff should at least consider the sentiments of the interviewee and bother to provide an update after taking so much time.

First round: Given a hierarchy of tasks, implement a multithreaded program to complete all tasks. Optimize as much as possible.

Second round: Given a buffer space, implement two queues using just that buffer as common memory space.

Third round: Given a cluster of nodes and ping logs, identify the nodes which haven't been pinged in the last k seconds.

Fourth round: Given a stream of integers, find the minimum difference considering only the last k integers.