Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques : 14th International Workshop, APPROX 2011, and 15th International Workshop, RANDOM 2011, Princeton, NJ, USA, August 17-19, 2011, Proceedings - Leslie Ann Goldberg, Klaus Jansen, R. Ravi, José D. P. Rolim ((Lecture Notes in Computer Science))