The most difficult is first tech interview, where you have only 1 hour to complete pretty difficult task. You'll need to work a lot with arrays, aggregate data, re-structure it and use properly to get required info. Also, the description of task is not so simple to understand after first read. You really need spend some time to understand requirements and clarify them with interviewer. I spend about 20min just reading it and discussing with interviewer before I wrote at least one useful line of code. Second tech interview was pretty straight forward, if you know how to act during design interviews. There were no any requirements, you needed to create requirements yourself for application, that you also choose yourself.