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

IntermediateRejected
Jul 2026

Summary

Spent weeks grinding leetcode and then got blindsided by a C++ templates question. Not a single algorithm in sight, just raw language syntax I'd never touched in a real job. Pretty sure I bombed it.

Questions Asked (1)

Q1

Implement a vector's push_back function using C++ templates (i.e., with a generic type T rather than a concrete type).

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The second I saw the T's I just kind of froze.

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AI HintsAI Generated

Suggested Approach

Clarify that you're implementing a simplified vector's push_back, then walk through the key operations: checking capacity, reallocating if needed, constructing the new element, and updating size. Emphasize exception safety and template genericity, and discuss trade-offs like growth factor and move semantics.

Pro tip: Mention that you'd use placement new and std::move_if_noexcept to provide strong exception safety, and that you'd leverage std::allocator for proper memory management—this shows you understand production-quality container implementation.

1. Clarify requirements and constraints

Confirm that the vector uses dynamic arrays, and discuss assumptions like growth strategy and exception guarantees. Ask if you should implement a full vector or just push_back in isolation.

2. Outline the algorithm

Describe the steps: check if size == capacity, if so allocate new memory (typically double capacity), move/copy existing elements, destroy old elements, and deallocate old memory. Then construct the new element in place and increment size.

3. Write the code with templates

Implement the function using template <typename T> and show proper use of placement new, std::move_if_noexcept, and allocator_traits. Handle self-assignment and exception safety.

4. Discuss trade-offs and optimizations

Explain choices like growth factor (1.5 vs 2), using move semantics when possible, and providing strong exception guarantee. Mention potential optimizations like reserving memory or using small buffer optimization.

5. Test and validate

Mention edge cases: pushing to empty vector, pushing after reserve, exception thrown during copy/move, and self-referential types. Suggest writing unit tests.

Key Points to Mention

  • Template syntax and generic type T
  • Capacity vs size and reallocation strategy
  • Placement new and explicit destructor calls
  • Exception safety guarantees (strong vs basic)
  • Move semantics and std::move_if_noexcept
  • Memory management with std::allocator

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