What I used to do when interviewing software engineers is letting them write a simple (but complete) program (not on paper but in actual IDE, compile, run, debug etc.). I used a command line game I invented where the player navigates a simple "labyrinth" of squares, but feel free to invent your own. Typically, the candidates took 1.5-2.5 hours to complete it.

This gives you a way better idea than programming puzzles: you see how they write real live code, how well they understand the requirements, how they test their code, how they use the debugger etc.