Letchworth State Park

This park is beautiful, especially in Fall. You're better hurry as the Fall is leaving soon.

Approximation Algorithms

1. Lecture notes on Approximation Algorithms by Chandra Chekuri
http://www.cs.uiuc.edu/homes/chekuri/teaching/fall2006/approx.htm
2. Using primal dual method for Approximation Algorithms, a good survey by David P. Williamson
The primal-dual method for approximation algorithms and its application to network design problems
3. Using Local Ratio method for Approximation Algorithms, a survey by Reuven Bar-Yehuda, Keren Bendel, Ari Freund, and Dror Rawitz
Local ratio: A unified framework for approximation algorithms
4. Some time it seems that whatever way we try, we just can find a approximation. Well, maybe computing good approximation for that problem is also NP-hard. To prove the hardness of approximation, following documents are good starting point:
A survey by Sanjeev Arora, and Carsten Lund
Hardness of approximations
Another one by Luca Trevisan
Inapproximability of Combinatorial Optimization Problems
For approximating minimization problems
On the hardness of approximating minimization problems