Documentation & Reference
These resources will provide you with information about syntax and standard libraries:
Java Documentation
C++ Standard Library
C++ Syntax
Stack Overflow
Java Documentation
C++ Standard Library
C++ Syntax
Stack Overflow
Algorithms and Data Structures
These resources discuss the theory behind the data structures and algorithms that are necessary for higher-level competitive programming:
Introduction to Algorithms (PDF)
GeeksForGeeks
A list of recommended topics can be found here.
Introduction to Algorithms (PDF)
GeeksForGeeks
A list of recommended topics can be found here.
Training
These websites offer training problems and explanations:
USACO Guide (free resource developed by Ben Qi)
USACO Training
Hackerrank
CodeChef
USACO Guide (free resource developed by Ben Qi)
USACO Training
Hackerrank
CodeChef