Combinatorics for Computer Science (Computers and math series) by Williamson, S. Gill (1985) Hardcover

This beginning graduate level text studies the use of geometric and algebraic structures to compare and classify combinatorial algorithms. The geometric concepts, in particular, are useful in both complexity analysis and practical programming. This book is on the creative commons (Google Books). Further discussion can be found at the website of the Department of Computer Science and Engineering, UCSD: http://cseweb.ucsd.edu/~gill/AlgCombSite/