There are many distinct pleasures associated with computer programming‎.‎ Craftsm‎- ship has its quiet rewards‎,‎ the satisfaction that comes from building a useful object and making it work‎.‎ Excitement arrives with the ‎?‎ash of insight that cracks a previously intractable problem‎.‎ The spiritual quest for elegance can turn the hacker into an artist‎.‎ Therearepleasuresinparsimony‎,‎insqueezingthelastdropofperformanceoutofclever algorithms and tight coding‎.‎ Thegames‎,‎puzzles‎,‎andchallengesofproblemsfrominternationalprogrammingc‎- petitionsareagreatwaytoexperiencethesepleasureswhileimprovingyouralgorithmic and coding skills‎.‎ This book contains over 100 problems that have appeared in previous programming contests‎,‎ along with discussions of the theory and ideas necessary to ‎- tack them‎.‎ Instant online grading for all of these problems is available from two WWW robot judging sites‎.‎ Combining this book with a judge gives an exciting new way to challenge and improve your programming skills‎.‎ This book can be used for self‎-study‎,‎ for teaching innovative courses in algorithms and programming‎,‎ and in training for international competition‎.‎ To the Reader Theproblemsinthisbookhavebeenselectedfromover1‎,‎000programmingproblemsat the Universidad de Valladolid online judge‎,‎ available athttp‎:‎//online‎-judge‎.‎uva‎.‎es‎.‎The judgehasruledonwelloveronemillionsubmissionsfrom27‎,‎000registeredusersaround the world to date‎.‎ We have taken only the best of the best‎,‎ the most fun‎,‎ exciting‎,‎ and interesting problems available‎.‎