Design an Indexable Deque with O(1) Access
Company: Hudson River Trading
Role: Software Engineer
Category: Software Engineering Fundamentals
Difficulty: hard
Interview Round: Technical Screen
Design a data structure backed by a deque that supports push front, push back, pop front, pop back, and O(1) access by logical index. Explain how an offset and index mapping can preserve stable logical indexing as elements are removed from the front.
### Constraints & Assumptions
- The operations are in memory.
- Logical indices refer to insertion positions unless clarified.
- O(1) average access is required.
- The exact language can provide deque iterators or array-like blocks.
### Clarifying Questions to Ask
- Should indices remain stable after pops?
- Are duplicate values allowed?
- Do we access by current position or original logical index?
- What should happen for removed indices?
- Are iterators invalidated by deque operations in the chosen language?
### What a Strong Answer Covers
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### Follow-up Questions
- How would you implement this without stable iterators?
- How would memory be reclaimed?
- How would concurrency affect the map and deque?
- How would random deletion by index work?
Quick Answer: This Hudson River Trading software engineering question asks candidates to design an indexable deque with constant-time access expectations. It is useful practice for data-structure trade-offs, API guarantees, and explaining when theoretical complexity meets practical implementation constraints.