I am trying to do well in this year's National Physics Olympiad here to qualify for the APhO and IPhO team. So I need to increase my skill of solving physics problems. What books are the best for physics problems and also teaches the problem solving skills??? I am already studying University Physics, Kleppner's Mechanics, Pedroti's Optics, Berkeley Physics Course(Electromagnetism). But is there any book that gives importance on problem solving like Physics olympiads that can increase my problem solving skills???