Dieter Jungnickel 
Graphs, Networks and Algorithms [PDF ebook] 

From the reviews of the German edition:"Combinatorial optimization, along with graph algorithms and complexity theory is booming. This book treats the most prominent problems which are polynomially solvable. The Traveling Salesman Problem is discussed as a paradigm of an NP-complete problem. The text is well written, most exercises are quite enlightening and the hints are clear. Algorithms are described very thoroughly. The list of references is impressive and gives good guidance for further reading.The book can be recommended to beginners as an introductory text as well as for research and industry as a reference."(OPTIMA)In this corrected 2nd printing of the first edition the author has made some small modifications: some minor mistakes were corrected and updates to the bibliography provided.