Not very difficult, but very good question.
On campus interview: rotation direction when in north pole, transcript a decimal number to binary number, test if a height-balanced BST, reconstruct to be a high-balanced BST, difficulty encountered
Coding test: airports questions, basically graph problems, Dijkstra's algorithm and DFS
Onsite interview: find angle difference of a time, triangle overlap, code optimization, implement hashtable insert and retrival, your goal, most stressed time, your favorite language, your project
