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Meta·Software Engineer·Technical Phone Screen·Senior

Senior
Apr 2026

Summary

Coding round at Meta for a Research Scientist position. Just one problem but it had enough nuance to keep me on my toes for a bit.

Questions Asked (1)

Q1

You have two linked lists where each node holds a string value. Determine whether the full strings formed by concatenating each list's nodes are identical.

Algorithms & Data Structures
Author's notes

My first instinct was to just collect all node values into two big strings and compare them.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem: each linked list represents a string formed by concatenating its nodes' string values. Then, discuss approaches to compare the concatenated strings efficiently, considering time and space complexity, and handle edge cases like empty lists or different lengths.

Pro tip: Mention that you can compare the strings on the fly without concatenating them fully, which avoids unnecessary memory usage and handles large lists gracefully. This shows you think about scalability and optimization.

1. Clarify the problem

Confirm that the concatenated strings should be compared for exact equality, and discuss edge cases such as empty lists, null nodes, or different total lengths.

2. Discuss naive approach

Explain that you could traverse each list, concatenate all node values into strings, and then compare the strings. Mention the time and space complexity: O(n + m) time and O(n + m) space.

3. Propose optimized approach

Suggest comparing the strings without full concatenation by traversing both lists simultaneously, comparing characters node by node, and handling cases where node boundaries don't align. This reduces space complexity to O(1).

4. Analyze complexity and trade-offs

Compare the naive and optimized approaches in terms of time and space, and discuss when each might be preferable (e.g., simplicity vs. memory constraints).

5. Handle edge cases and test

Walk through examples like identical lists, different lengths, empty strings, and lists with varying node string lengths to ensure correctness.

Key Points to Mention

  • Time and space complexity of concatenation vs. on-the-fly comparison
  • Handling node boundaries when comparing character by character
  • Edge cases: empty lists, null nodes, different total lengths
  • Potential for early termination when a mismatch is found
  • Trade-offs between simplicity and memory efficiency
  • Use of two pointers to traverse lists simultaneously

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