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Apple·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Apple SWE interview, got asked to design an iterator. Not much else to go on but it was a coding/design type question.

Questions Asked (1)

Q1

Design an iterator.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

Pretty open-ended, which I wasn't expecting.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: what data structure is being iterated (e.g., array, tree, graph), what language, and whether it's a simple iterator or a more complex one like a binary search tree iterator. Then design the iterator class with state (e.g., index, stack) and implement hasNext() and next() methods, discussing time and space complexity trade-offs. Finally, consider edge cases and potential follow-ups like lazy evaluation or thread safety.

Pro tip: Demonstrate Apple's attention to detail by discussing memory management (e.g., avoiding unnecessary copies) and performance implications, especially for large data sets. Also, mention how your design would integrate with Apple's existing frameworks (e.g., Swift's IteratorProtocol) to show platform awareness.

1. Clarify Requirements

Ask questions to understand the scope: what data structure, language, and constraints (e.g., memory, thread safety). Confirm the expected interface (e.g., hasNext(), next()).

2. Design the Iterator

Choose an appropriate internal state representation (e.g., index for arrays, stack for trees) and outline the class structure. Explain how hasNext() and next() will work.

3. Analyze Complexity

Discuss time and space complexity for each operation, and any trade-offs (e.g., pre-processing vs. lazy evaluation).

4. Handle Edge Cases

Consider empty data, single element, calling next() when no elements remain, and concurrent modification. Explain how your design handles these.

5. Discuss Extensions

Mention potential follow-ups: supporting remove(), bidirectional iteration, or adapting to different data structures. Show awareness of language-specific idioms.

Key Points to Mention

  • State management: how you track the current position (e.g., index, pointer, stack).
  • Time and space complexity of hasNext() and next(), and overall memory usage.
  • Lazy evaluation vs. eager pre-processing, and when each is appropriate.
  • Thread safety and concurrent modification considerations.
  • Language-specific implementations (e.g., Java Iterator, Swift IteratorProtocol, Python generator).
  • Edge cases: empty collection, single element, multiple calls to next() after exhaustion.

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