Although I did not reached the interview stage, I was invited to a coding challenge. I feel that is important to know what this challenge means. It is basically a normal algorithmic problem (nothing much to do, just a sort) but the way the problem is described makes it very complicated. You get to spend a lot of time trying to understand the question just to realise that the question is fairly easy, but the description of the problem is very long and hard to understand and hard to choose what data structures are best to use. They give you raw input and you most probably have to parse it somehow, and this takes time too. Overall, the coding challenge was a negative experience for me. I could not complete it in the 75 minutes limit. I would advise you to be very quick with everything, including reading the problem and understand it and thinking about all corner cases in advance.