Stacks and Queues in Practice

Explain the difference between a stack and a queue, and where each shows up in real systems.

Your answer should cover:

1. The access discipline of each (LIFO vs FIFO) and their core operations.
2. Two real examples where a stack is the natural fit, and why the problem demands LIFO.
3. Two real examples where a queue is the natural fit, and why the problem demands FIFO.
4. How each can be implemented efficiently (what structure underneath, and what can go wrong naively).