This is an excellent training source in combinatorics for mathematics olympiads and contests.
Problems in this book are divided into 2 sets, with each set containing 51 problems. Problems in the first set are introductory ones (hence, relatively easy), and that in the second set are advanced problems (And harder, much harder indeed in the last few problems). Problems are very well selected and carefully organized according to their difficulty and technic involved. They span from the very easy first some enumerative problems to the really hard IMO-level, even notorious National-MO problems. Moreover, problems are up-to-date hence it avoids well-known cliche problems. The book is published in the end of 2002, and in this book some of the 102 problems are selected from the IMO that year!
As a regular lecturer of Taiwan's IMO team, I highly recommend this problem book.
