What is the difference between a stack and a queue?
This question evaluates your understanding of basic data structures and your ability to explain how they work. Instead of just giving definitions, it's helpful to discuss operation principles, common use cases, and key behaviors like insertion and removal.
Answer 1: Basic conceptual difference
English
A stack is a data structure that follows the Last In, First Out (LIFO) principle — the last element added is the first one to be removed. You can think of it like a stack of plates: you take the top plate first.
A queue, on the other hand, follows the First In, First Out (FIFO) principle — the first element added is the first one removed. It works like a line at a ticket counter or a waiting list.
Both are used to manage ordered data, but their access patterns are different. Stacks are useful for undo functionality or backtracking, while queues are commonly used for task scheduling, event handling, or data streaming.
Key Expressions
- Last In, First Out (LIFO): the most recently added item is removed first
- First In, First Out (FIFO): the earliest added item is removed first
- access pattern: the order in which elements are accessed or removed
- task scheduling: assigning tasks in order based on availability or time
- event handling: processing events in the order they occur
Answer 2: Operational behavior and use cases
English
The main difference between a stack and a queue lies in how items are added and removed.
In a stack, both operations happen at the same end — the top. The two main operations are push (add an item) and pop (remove the top item). You only have access to the last item added.
In a queue, items are added at the rear and removed from the front, preserving the order. The operations are enqueue (add an item to the end) and dequeue (remove the item from the front).
Stacks are commonly used for things like expression evaluation, undo systems, and recursive function calls. Queues are useful in breadth-first search (BFS), print jobs, and task queues.
Key Expressions
- push / pop: stack operations to add and remove items
- enqueue / dequeue: queue operations to add and remove items
- rear / front: the end where items are added (rear) and removed (front) in a queue
- task queue: a list of tasks to be processed in order
- print job: a request sent to a printer, processed in order
- BFS traversal: a graph or tree traversal technique using a queue
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