Verkada Inc.·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026Remote

Summary

Verkada coding screen for a software engineer role. One problem the whole time, linked list addition but with a twist that made me second-guess everything I thought I knew about the classic LC version.

Questions Asked (1)

Given two non-negative integers represented as linked lists where each node stores up to 4 decimal digits, return their sum as a linked list in the same format.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I've done the single-digit version enough times that I jumped in fast, which was probably a mistake.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints and edge cases, then propose a digit-by-digit addition approach that handles carries, leveraging the 4-digit chunking to optimize. Discuss trade-offs between iterative and recursive solutions, and analyze time/space complexity.

Pro tip: Mention that you would test with edge cases like different lengths, carries propagating across chunks, and leading zeros to ensure robustness. This shows attention to detail and quality.

1. Clarify Requirements and Constraints

Ask about input size, whether lists can be empty, if leading zeros are allowed, and if the sum should be in-place or a new list. Confirm that each node stores up to 4 digits (0-9999).

2. Design the Algorithm

Traverse both lists simultaneously, adding corresponding chunks along with any carry. Handle different lengths by continuing with the remaining list. Propagate carry to the next chunk.

3. Handle Edge Cases

Consider cases where one list is longer, carry propagates beyond the last node, and sums like 9999+1 produce a new node. Also handle empty lists and leading zeros in the result.

4. Analyze Complexity and Trade-offs

Discuss time complexity O(max(m,n)) and space complexity O(max(m,n)) for the result. Compare iterative vs recursive approaches and in-place vs new list creation.

5. Test and Validate

Walk through examples like 1234+5678, 9999+1, and lists of different lengths. Verify carry handling and that the result is correctly formatted.

Key Points to Mention

Carry propagation between chunks, especially when sum exceeds 9999
Handling lists of different lengths by padding with zeros or iterating until both are exhausted
Time and space complexity analysis: O(max(m,n)) time and space
Trade-offs between iterative and recursive solutions, and between modifying input vs creating new list
Edge cases: empty lists, carry beyond most significant chunk, leading zeros
Potential optimization: using a dummy head to simplify result list construction

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