Shafi Goldwasser, Silvio Micali, and Charles Rackoff. The knowledge complexity of interactive proof systems. Testing of the long code and hardness for clique. Some optimal inapproximability results. Oscar H. Ibarra and Chul E. Kim.
Fast approximation algorithms for the knapsack and sum of subset problems.
Russell Impagliazzo and David Zuckerman. How to recycle random bits. David S. Johnson. Approximation algorithms for combinatorial problems. David R. Karger, Rajeev Motwani, and G. D. S. Ramkumar.