It's implementing a messaging app? Tiny URL? A different one? What you think is the most challenging one and why?
Tiny url is not simple. The basic might be but the follow up questions can be tricky. Depends totally on the interviewer.
Ask a follow up question that is tricky?
I've found distributed scheduling slightly difficult
What’s so hard about Tiny URL? Sheesh... that one is pretty darn simple.
What for you is a challenging one?
Design Facebook post searching that supports Boolean operators for keywords.