# Design an object-oriented queue and compare implementations You are asked to design an object-oriented **Queue** abstraction and discuss how it can be implemented internally in different ways. Describe: 1. **Queue interface** - Define a clean, language-agnostic interface (or abstract class) for a generic FIFO queue. - Include the core operations and their expected behavior (e.g., `enqueue`, `dequeue`, `peek`, `isEmpty`, `size`, and possibly capacity-related methods). 2. **Internal implementations** For the same Queue interface, describe at least **two or three different internal data-structure implementations**, such as: - Linked-list-based queue - Array-based queue (including circular array/buffer) - Queue implemented using two stacks 3. **Trade-offs analysis** For each implementation, analyze and compare: - Time complexity of core operations (`enqueue`, `dequeue`, `peek`) - Space usage and overhead - Memory behavior (e.g., cache friendliness, allocations) - Practical pros/cons and when you would choose each approach Optionally, also discuss how you might extend the design for: - A **bounded** vs **unbounded** queue - **Thread-safe** vs **non-thread-safe** versions - How you would expose these variants via interfaces/classes (e.g., using different implementations behind the same Queue interface). ### Clarifying Questions to Ask - Clarify language/runtime assumptions and the level of depth expected. - Use examples to connect definitions to practical engineering decisions. - Call out pitfalls, trade-offs, and common misconceptions. ### What a Strong Answer Covers - Accurate definitions and comparisons with concrete examples. - Complexity, lifecycle, safety, or operational implications where relevant. - Trade-offs that explain when one approach is preferable to another. - Common failure modes and how to avoid them. ### Follow-up Questions - How would you debug a production issue related to this topic? - What trade-off would change in a high-throughput service? - Which misconception do candidates often have here?