Hiring engineers is hard, and companies haven't really figured it out yet. Even the best companies rely on puzzles and gimmicks that often have little to do with day-to-day programming.

At one company I interviewed with, I was asked to implement a queue using two stacks. At that time in my programming career, I had worked with C, C++, Obj-C, Lua, Python, JavaScript, SQL, and a handful of DSLs developing games, game development tools, and web applications. Want to know what I had never done? Written a queue using two stacks. My immediate response to the question was, "Why would you want to do that?"

If you really want to know if someone has the capacity to pull their weight as an engineer, ask them about what they've built. Even if they are fresh out of college, the best engineers will have projects they can talk about and explain. Ask how they approached/solved specific problems. Ask what they're most proud of building. Ask what was most frustrating.

Those are the kind of questions that will provide insight into a person's problem solving capabilities and offer a decent picture of what they're capable of doing.