Data structure and algorithm questions can be more or less like riddles though. For example, the question about finding a loop in a singly linked list is a bit

Data structure and algorithm questions can be more or less like riddles though. For example, the question about finding a loop in a singly linked list is a bit like a riddle. There is also one about writing out a binary tree layer by layer, which really amounts to: "do you know what breadth-first traversal is, and do you get the insight that you can do that on trees too?"