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Bytedance·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Bytedance software engineer screen, just one coding problem on linked lists. Pretty standard stuff but they pushed on the space complexity angle which I wasn't fully ready for.

Questions Asked (1)

Q1

Reverse a singly linked list in-place and return the new head. Be prepared to implement both an iterative and a recursive solution and explain the space complexity difference between them.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The reversal itself wasn't the hard part.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (e.g., in-place, return new head) and then walk through the iterative solution step-by-step, emphasizing pointer manipulation. Follow with the recursive solution, highlighting the call stack and space complexity difference. Conclude by comparing trade-offs and mentioning edge cases.

Pro tip: During implementation, use a dummy node or draw the pointers on a whiteboard to avoid losing references; this shows attention to detail and reduces bugs. Also, explicitly state that the recursive solution uses O(n) space due to call stack, while iterative is O(1).

1. Clarify requirements and edge cases

Confirm that the list is singly linked, in-place means no extra nodes, and return the new head. Discuss edge cases: empty list, single node, two nodes.

2. Explain iterative approach

Describe using three pointers (prev, curr, next) to reverse links one by one. Walk through the loop invariant and termination condition.

3. Implement iterative solution

Write clean code for the iterative method, handling edge cases. Mention that it runs in O(n) time and O(1) space.

4. Explain recursive approach

Describe the recursive strategy: recursively reverse the rest of the list and then adjust pointers. Highlight the base case (empty or single node).

5. Compare space complexity and trade-offs

Contrast iterative O(1) space with recursive O(n) space due to call stack. Discuss when recursion might be preferred (e.g., simplicity) despite space overhead.

Key Points to Mention

  • Iterative solution uses three pointers (prev, curr, next) and reverses links in a single pass.
  • Recursive solution reverses the rest of the list and then adjusts the head's next pointer.
  • Space complexity: iterative is O(1), recursive is O(n) due to call stack.
  • Time complexity for both is O(n).
  • Edge cases: empty list, single node, and ensuring the new head is returned correctly.
  • In-place means no additional data structures; only pointer manipulation.

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