Tml·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Had a technical screen at Tml for a Software Engineer role. The whole thing was basically one meaty implementation problem around a deque backed by a circular array, which sounds manageable until you're actually writing resize logic under pressure.

Questions Asked (1)

Implement a double-ended queue backed by a circular array. It should support push and pop from both ends, peek operations, isEmpty, size, and automatically resize when the underlying array fills up. All operations should be O(1) amortized.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The circular part is where I lost some time.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases, then explain the circular array design with head/tail indices and modular arithmetic. Walk through the implementation of each operation, emphasizing O(1) amortized resizing via array doubling, and discuss trade-offs compared to a linked list.

Pro tip: Mention that you would use a power-of-two capacity to replace modulo with bitwise AND for performance, and note that resizing should be amortized by doubling and halving to avoid thrashing.

1. Clarify requirements and constraints

Ask about expected data types, thread-safety, and whether the queue should be bounded. Confirm that all operations must be O(1) amortized and that resizing is required.

2. Design the circular array structure

Explain using a fixed-size array with head and tail indices, and a size counter. Use modular arithmetic to wrap around, and define empty/full conditions.

3. Implement core operations

Detail push/pop from both ends, peek, isEmpty, and size. Show how head and tail are updated and how size is maintained.

4. Handle resizing

Describe doubling capacity when full and optionally halving when size is 1/4 of capacity. Explain how to copy elements in order to the new array and reset indices.

5. Analyze complexity and trade-offs

Argue O(1) amortized for push/pop, O(1) for peek/isEmpty/size. Compare with linked list implementation, noting cache efficiency and memory overhead.

Key Points to Mention

Use of head and tail indices with modular arithmetic to achieve circular behavior.
Maintain a size variable to distinguish between empty and full states.
Resizing strategy: double capacity when full, optionally halve when size is 1/4 capacity to avoid thrashing.
Amortized O(1) analysis: resizing cost is amortized over many operations.
Edge cases: empty queue pop/peek, resizing when empty, and handling wrap-around correctly.
Trade-offs: circular array vs linked list (cache locality, memory overhead, complexity).

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