written by Antti Laaksonen
|Competitive Programmer's Handbook is a free online book whose purpose is to give the reader a thorough introduction to competitive programming. You can download the book here (PDF) and view the project on GitHub.
|Guide to Competitive Programming is a printed book, published by Springer. It is based on Competitive Programmer's Handbook, but also discusses more advanced topics. You can buy the book, for example, through Springer or Amazon.
|Олимпиадное программирование (Olympiad Programming) is a Russian version of Guide to Competitive Programming, published by DMK Press. You can find more information about the book on their website.
|알고리즘 트레이닝: 프로그래밍 대회 입문 가이드 is a Korean version of Guide to Competitive Programming, published by Insight Book. You can find more information about the book on their website.
Do you want to practice competitive programming? The CSES Problem Set contains a collection of practice problems, ranging from easy to difficult.