Bytedance·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

May 2026Remote

Summary

Bytedance coding round, one algorithmic problem about linked lists. Pretty niche problem type, not your typical easy-medium grind.

Questions Asked (1)

Given the head of a linked list, reverse the nodes within each group of even length. The list is split into groups of sizes 1, 2, 3, 4, and so on. Reverse a group if its size is even, leave it alone if odd. The last group might be smaller than expected, but the rule still applies based on its actual size.

Algorithms & Data Structures

Author's notes

I'd seen linked list reversal before but never with this grouping twist.

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AI HintsAI Generated

Suggested Approach

Clarify the problem and edge cases, then propose an iterative in-place solution that traverses the list while tracking group boundaries and sizes. For each group, determine its actual size, and if even, reverse the nodes within that group by adjusting pointers; otherwise, skip. Finally, reconnect the reversed groups and return the new head.

Pro tip: Emphasize the importance of handling the last group correctly and maintaining O(1) space; also mention that you would write unit tests for edge cases like empty list, single node, and groups of varying sizes.

1. Understand the problem and clarify edge cases

Restate the problem to ensure alignment, and ask about constraints (e.g., list length, memory limits). Discuss edge cases: empty list, single node, last group smaller than expected.

2. Design the algorithm

Plan an iterative approach with a dummy node to simplify head changes. Use pointers to track the start and end of each group, and a counter to determine group size. For each group, if size is even, reverse the nodes; otherwise, skip.

3. Implement the reversal logic

Write a helper function to reverse a sublist of given size, or inline the reversal by adjusting next pointers. Ensure proper reconnection of the reversed group with the previous and next groups.

4. Handle the last group and termination

After processing all full groups, check if the remaining nodes form a group of even size. If so, reverse them; otherwise, leave as is. Ensure the list is properly terminated.

5. Analyze complexity and test

State time complexity O(n) and space O(1). Walk through examples, including edge cases, to verify correctness. Mention potential pitfalls like pointer loss during reversal.

Key Points to Mention

Use of dummy node to simplify edge cases (e.g., reversing the first group).
Tracking group boundaries with pointers (prev, start, end) and group size.
In-place reversal to achieve O(1) space complexity.
Handling the last group based on its actual size, which may be smaller than the expected group size.
Time complexity O(n) and space complexity O(1).
Testing with edge cases: empty list, single node, groups of even/odd sizes, and last group of even size.

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