The Art of Computer Programming (TAOCP) - http://www-cs-staff.stanford.edu/~knuth/taocp.html By Donald E. Knuth. Bibliographic details of the published volumes (1-3, various editions and translations) and on-line beta versions of parts of volume 4, "Combinatorial Algorithms".
Algorithms and Complexity - http://www.math.upenn.edu/~wilf/AlgComp.html A downloadable textbook by Herbert S. Wilf. Each chapter is available as compressed PostScript or PDF.
A Compendium of NP Optimization Problems - http://www.nada.kth.se/~viggo/wwwcompendium/ By P. Crescenzi and V. Kann; KTH Stockholm. A continuously updated version of the appendix from the book "Complexity and Approximation" (Springer, 1999).
Handbook of Algorithms and Data Structures - http://www.dcc.uchile.cl/~rbaeza/handbook/hbook.html By Gaston H. Gonnet and Ricardo Baeza-Yates. The preface, table of contents, index and all source code of this handbook. The main goal is to make available through Internet the source code of many algorithms (in C and/or Pascal) that have been already tested.
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