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Early-stage Startup·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Coding round for a software engineer role, just one question but it had some depth to it. Not a ton of context in the prompt but the implementation details kept things interesting.

Questions Asked (1)

Q1

Implement a deque (double-ended queue) from scratch, including automatic resizing when the underlying storage is full.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

I started with a fixed-size circular buffer which felt right, but the resize logic tripped me up more than I expected.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, then outline the deque's core operations and how you'll implement them using a circular buffer with dynamic resizing. Walk through the resizing logic, discuss time complexity, and mention edge cases and potential optimizations.

Pro tip: Discuss the trade-offs between different resizing strategies (e.g., doubling vs. incremental) and how they affect amortized time complexity. Also, mention that you'd consider using a doubly linked list as an alternative, but highlight why a dynamic array is often preferred for cache efficiency.

1. Clarify Requirements and Constraints

Ask about expected operations (push/pop from both ends), performance requirements, memory constraints, and whether thread safety is needed. This shows you think before coding.

2. Choose Data Structure and Design

Propose using a circular dynamic array for O(1) amortized operations and good cache locality. Explain how you'll track front and back indices and size.

3. Implement Core Operations

Describe push_front, push_back, pop_front, pop_back, and peek operations, handling wrap-around using modulo arithmetic. Mention edge cases like empty deque.

4. Implement Dynamic Resizing

Explain when to resize (when full) and how (allocate new array of double capacity, copy elements in order). Discuss shrinking to avoid wasted memory.

5. Analyze Complexity and Test

State time complexity: O(1) amortized for push/pop, O(n) for resize. Discuss testing strategies including unit tests for edge cases and performance benchmarks.

Key Points to Mention

  • Circular buffer implementation with head and tail pointers
  • Amortized O(1) time complexity for push/pop operations
  • Resizing strategy: double capacity when full, halve when quarter full to avoid thrashing
  • Handling wrap-around using modulo arithmetic
  • Edge cases: empty deque, full deque, resizing during operations
  • Trade-offs: dynamic array vs. doubly linked list (cache efficiency vs. memory overhead)

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.