Data structures for weighted matching and nearest common ancestors with linking. M. R. Garey, R. L. Graham, and D. S. Johnson. Some NP-complete geometric problems. Michelangelo Grigni, Elias Koutsoupias, and Christos Papadimitriou. Oscar H. Ibarra and Chul E. Kim.
Fast approximation algorithms for the knapsack and sum of subset problems.
Narendra Karmarkar and Richard M. Karp. Joseph S. B. Mitchell. Christos H. Papadimitriou. The Euclidean Traveling Salesman Problem is NP-complete. Christos H. Papadimitriou and Mihalis Yannakakis.