OOP Concepts: Inheritance, Polymorphism, Encapsulation, Abstraction.
2 Memory: Pointers, References, Smart Pointers (unique_ptr, shared_ptr).
3 STL: vector, map, set, queue, stack.
4 Copy Constructor, Operator Overloading, Virtual Functions.
5 RAII concept & Exception Handling.
6 Common Qs: Reverse string, LRU cache, duplicate.