I do not feel that I should disclose the actual questions, but they were definitely the most fair of any interview I received. I felt like it was super positive environment where they want you to succeed. Make sure you are familiar with basic data structures (stacks, queues, graphs, trees, etc) and your classical n log n sorting algorithms (merge sort is a great one to know for every interview not just Yelp). They also give you a lot of opportunities to show that you know things. Just go with. Verbalize your thoughts and tell tidbits of knowledge along the way. But get code on the board. I feel like Yelp really wanted working code on the white board, and you have a very limited amount of time. Practice on an actual whiteboard with an engineer before if you can. Whiteboarding is never the easy. Seriously check your markers between interviews or bring your own. There is nothing worse than a marker going out during thoughts.
I have heard that someone asks you to make a search engine (preprocess and make files into an inverted index) for Web Dev interviews, but that was not the case for mine :)