DURHAM -- Duke is undefeated, 15-0, and ranked No. 1 in the country. But because of Ryan Kelly’s injury, the offense is undergoing a major overhaul. Replacing Kelly isn’t as simple as inserting another player into his spot, as the Blue Devils don’t have another option with his combination of size and 3-point shooting ability. When Duke tips off at No. 20 N.C. State at noon Saturday, it will be Quinn Cook who attempts to fill most of the offensive void.