First I received a call from a recruiter asking me to finish a hackerRank test. I got it pretty fast. It was a hashmap problem. Then scheduled a skype call with an Yelp Engineer who asked me to solve a Graph topological problem. I wasn't very sure about topological sort and the whole process was just less than 20 mins so I briefly use a method to sort the graph and then do a BFS traversal to construct the tree.