Math Olympiad
I am a math Olympiad enthusiast and still try to solve Olympiad problems whenever I get time.
India secured 4th position at IMO 2024 (India's best rank so far!)
Books Recommendations:
Introductory Books:
Dmitrii Vladimirovich Fomin, Ilia Itenberg, and Sergei Aleksandrovich Genkin - Mathematical Circles: Russian Experience (1996).
M. R. Modak S. A. Katre - An Excursion In Mathematics (2018).
Inequalities:
Zdravko Cvetkovski - Inequalities Theorems, Techniques and Selected Problems (2012).
B.J. Venkatachala - Inequalities: An Approach Through Problems (2009).
Functional Equations:
Pang-Cheng, Wu - Functional Equation (2018). Link.
Combinatorics:
Titu Andreescu and Zuming Feng - A Path to Combinatorics for Undergraduates (2004).
Pablo Soberón - Problem-Solving Methods in Combinatorics An Approach to Olympiad Problems (2013).
Chuan Chong Chen and Koh Khee Meng - Principles and Techniques in Combinatorics (1992).
Daniel A Marcus - Combinatorics: A Problem Oriented Approach (1998).
Number Theory:
Justin Stevens - Olympiad Number Theory Through Challenging Problems (2016).
David M. Burton - Elementary Number Theory (2010).
Dorin Andrica and Titu Andreescu - Number Theory: Structures, Examples, and Problems (2009).
Titu Andreescu, Gabriel Dospinescu, and Oleg Mushkarov - Number Theory: Concepts and Problems (2017).
Ion Cucurezeanu, Dorin Andrica, Titu Andreescu - An introduction to Diophantine equations: A problem-based approach (2010).
Michael Th. Rassias - Problem-Solving and Selected Topics in Number Theory: In the Spirit of the Mathematical Olympiads (2010).
Geometry:
Kiran S. Kedlaya - Geometry Unbound (2006).
H. S. M. Coxeter, Samuel L. Greitzer - Geometry revisited (1996).
Haibin Wang and Kim Hoo Hang - Solving Problems in Geometry: Insights and Strategies for mathematical olympiad (2018).
Evan Chen - Euclidean Geometry in Mathematical Olympiads (2016).
Problem-Solving:
Paul Zeitz - The art and craft of problem solving (2017).
Derek Holton - A first step to Mathematical Olympiad problems (2010).
Great resources(Links):
A compiled version of IMO longlist Problems of previous years from 1959-2004.
Some book pdfs are available here.
Carnegie Mellon Informatics and Mathematics Competition (CMIMC)