Meta·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Meta SWE coding round, just the one question but it had enough edge cases to keep me busy. String parsing stuff that looks easy until you actually sit down and code it up.

Questions Asked (1)

Implement a function that converts a string to a 32-bit signed integer, handling leading whitespace, optional sign characters, non-digit characters mid-string, and integer overflow clamping.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

The overflow clamping part is where I fumbled.

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AI HintsAI Generated

Suggested Approach

Clarify the exact rules for whitespace, sign, digits, and overflow, then walk through a single-pass parsing algorithm that builds the integer while checking bounds. Emphasize edge cases and how you would test them, and discuss trade-offs between different approaches.

Pro tip: Mention that you can avoid using 64-bit integers by checking overflow before multiplying or adding, which is important in languages like C++ or Java where overflow behavior is defined. Also, explicitly state how you handle the case where no digits are found (return 0).

1. Clarify requirements and edge cases

Ask about whitespace handling (only leading?), sign characters (multiple?), non-digit characters (stop parsing?), and overflow behavior (clamp to INT_MAX/INT_MIN). Confirm that if no digits are parsed, return 0.

2. Outline the algorithm

Describe a single-pass approach: skip leading whitespace, read optional sign, then iterate through digits, updating the result and checking for overflow before each update.

3. Detail overflow handling

Explain how to check for overflow without using larger types: before multiplying by 10, compare with INT_MAX/10 and check the last digit; similarly for negative numbers with INT_MIN.

4. Walk through examples

Trace through test cases like ' -42', '4193 with words', 'words and 987', '-91283472332', and '+-12' to demonstrate correctness and edge case handling.

5. Discuss complexity and trade-offs

State O(n) time and O(1) space. Mention alternative approaches (e.g., using regex or built-in parsing) and why manual parsing is preferred for control and efficiency.

Key Points to Mention

Leading whitespace only; ignore all other whitespace.
Optional single sign character ('+' or '-') before digits.
Stop parsing at first non-digit character; ignore rest of string.
Overflow clamping to INT_MAX (2147483647) or INT_MIN (-2147483648).
Return 0 if no digits are parsed.
Time complexity O(n), space complexity O(1).

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