Arista Networks·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Coding round at Arista Networks for a software engineer position. Pretty standard stuff, one algorithm question with a follow-up on complexity. Nothing too wild but they did push on edge cases more than I expected.

Questions Asked (1)

Write a function to check if a string is a palindrome. Make sure to handle empty strings and null input, then walk through the time and space complexity of your solution.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I jumped straight into the logic and forgot about null for an embarrassingly long time.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and edge cases (null, empty string, case sensitivity, non-alphanumeric characters). Then present a two-pointer solution that compares characters from both ends moving inward, handling null and empty inputs upfront. Finally, analyze time and space complexity, noting O(n) time and O(1) space for the iterative approach.

Pro tip: Mention that you can optimize by only traversing half the string and that early termination on mismatch improves average-case performance. Also, discuss trade-offs between iterative and recursive solutions, highlighting recursion's O(n) space overhead.

1. Clarify requirements and edge cases

Ask if the palindrome check should ignore case, spaces, and punctuation, and confirm how to handle null and empty strings. State assumptions clearly.

2. Outline the algorithm

Describe the two-pointer technique: initialize left at 0 and right at length-1, compare characters, and move pointers inward until they meet or cross.

3. Handle edge cases

Explicitly handle null (return false or throw exception) and empty string (return true). Optionally, normalize the string by removing non-alphanumeric characters and converting to lower case.

4. Implement the function

Write clean code with meaningful variable names, ensuring the loop condition is correct and early exit on mismatch.

5. Analyze complexity

State that time complexity is O(n) because each character is visited at most once, and space complexity is O(1) for the iterative two-pointer approach (excluding input storage).

Key Points to Mention

Two-pointer technique for O(n) time and O(1) space
Handling null and empty string explicitly
Case sensitivity and non-alphanumeric character handling (if required)
Early termination on mismatch for efficiency
Comparison of iterative vs recursive approaches (recursion uses O(n) space)
Potential optimization: only traverse half the string

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