You have a data structures exam coming up, or your CS class just hit stacks and queues and the textbook lost you three pages in. This guide is the shortcut.

**TLDR: Stacks and Queues** covers everything a high school or early college student needs to understand, implement, and apply these two foundational data structures — in under 20 pages. You'll learn the difference between LIFO and FIFO, work through the full API for both structures, see array and linked-list implementations with real code, and understand why the naive array queue is slow and how a circular buffer fixes it. The guide also covers deques and priority queues, then closes with the canonical real-world problems — balanced parentheses, undo functionality, breadth-first search, the call stack, and task scheduling — so you can recognize a stack or queue problem the moment you see one.

This is an intro to data structures for college students and advanced high school learners who want clarity fast. No padding, no lengthy theory — just the concepts, the code, and the worked examples you need. It's also a solid resource if you're searching for a data structures study guide for high school CS or AP Computer Science Principles review.

If you want to walk into your next class or exam knowing exactly how these structures work and where they appear, pick this up and read it in one sitting.

• Explain the LIFO and FIFO access rules and when each is appropriate
• Implement a stack and a queue using arrays and linked lists, and reason about their time complexity
• Recognize stack and queue patterns in real problems like undo, expression evaluation, BFS, and scheduling
• Use specialized variants — deques, circular queues, priority queues, and the call stack — with confidence
• Solve standard interview-style problems involving stacks and queues

1. 1. What Stacks and Queues Actually Are
   Introduces both structures by analogy and contrasts LIFO with FIFO using everyday examples.
2. 2. The Stack: Operations, Implementation, and Complexity
   Covers the full stack API, implements it with both an array and a linked list, and analyzes performance.
3. 3. The Queue: Operations, Implementation, and the Circular Buffer Trick
   Builds the queue API, shows why a naive array implementation is slow, and fixes it with a circular buffer.
4. 4. Variants You Should Know: Deques and Priority Queues
   Introduces double-ended queues and priority queues, what they add, and where they get used.
5. 5. Where They Show Up: Real Problems and Algorithms
   Walks through canonical applications — balanced parentheses, expression evaluation, undo, BFS, the call stack, and scheduling.