360 Problems for Mathematical Contests
by Titu Andreescu and Dorin Andrica
GIL Publishing House, Romania | 2003 | ISBN-10: 9739417124 | DJVU/PDF | 280 pages | 2/12.1 mb 
https://www.amazon.com/Problems-Mathematical-Contests-Titu-Andreescu/dp/9739417124
PDF conversion is mine.

This book is intended to help students preparing for all rounds of Mathematical Olympiads or any other significant mathematics contest.
This book is the fruit of a prodigious activity of the two authors, well-known creators of mathematics questions for Olympiads and other mathematical contests. They have published innumerable original problems in various mathematical journals.
The book is organized in six chapters: algebra, number theory, geometry, trigonometry, analysis and comprehensive problems. In addition, other fields of mathematics found their place in this book, for example, combinatorial problems can be found in the last chapter, and problems involving complex numbers are included in the trigonometry section. Moreover, in all chapters of this book the serious reader can find numerous challenging inequality problems. All featured problems are interesting, with an increased level of difficulty; some of them are real gems that will give great satisfaction to any math lover attempting to solve or even extend them.