Course in Combinatorics

Combinatorics, a subject dealing with ways of arranging and distributing objects, involves ideas from geometry, algebra, and analysis. The breadth of the theory is matched by that of its applications, which include topics as diverse as codes, circuit design and algorithm complexity. It has thus become an essential tool in many scientific fields. In this second edition the authors have made the text as comprehensive as possible, dealing in a unified manner with such topics as graph theory, extremal problems, designs, colorings, and codes. 

Secret Codes (Penguin Active Reading Series - Level 4 Intermediate)
For thousands of years people have used codes and ciphers to keep secrets from people who will do anything to learn them. How did secret messages cause a queen to lose her head? How have lost languages finally been understood? How did one little-known language help a country win a war? Read this book and find out.