Stacks & Queues

LIFO and FIFO with arrays and linked lists, the circular queue, and the STL containers.

1. 5.1Stacks with an ArrayLast in, first out. The stack ADT (push, pop, peek, isEmpty, isFull) built on a fixed array with a top index, plus overflow and underflow. 45 mineasy
2. 5.2Stacks with a Linked ListThe same stack ADT, but the top is the head of a linked list. No fixed capacity, push and pop stay O(1), and the bracket-matching application. 35 mineasy
3. 5.3Queues with an ArrayFirst in, first out. Why a naive array queue makes dequeue O(n), how a front index makes it O(1), and the wasted-slot problem that leads to the circular queue. 40 mineasy
4. 5.4Queues with a Linked ListKeep two pointers, front and rear. Enqueue at the rear and dequeue at the front, both O(1), with no capacity limit. 30 mineasy
5. 5.5Circular QueueLet front and rear wrap around with the modulo operator, so freed slots are reused. All operations O(1) on a fixed array. 40 minmedium
6. 5.6std::stack, std::queue & std::dequeThe standard library versions you will use in real code and on LeetCode, their method names, and the classic traps (pop returns void, empty checks). 25 mineasy