Bloomberg·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Bloomberg SWE interview with a classic string parsing problem. Nothing flashy, but the edge cases will trip you up if you're not careful.

Questions Asked (1)

Implement the atoi function: convert a string to a 32-bit signed integer, handling leading whitespace, optional sign characters, non-digit terminators, and clamping to the 32-bit signed integer range.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I thought I had this nailed in the first two minutes and then spent the rest of the time patching edge cases.

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AI HintsAI Generated

Suggested Approach

Clarify the exact rules for whitespace, sign, and overflow handling, then implement a single-pass parser that builds the integer digit by digit while checking for overflow before each multiplication and addition. Use 32-bit bounds (INT_MIN and INT_MAX) and clamp the result if overflow occurs.

Pro tip: Mention that you would use a 64-bit accumulator to simplify overflow detection, but still clamp to 32-bit bounds—this shows awareness of practical implementation trade-offs. Also, explicitly state that you would test edge cases like empty string, only whitespace, sign without digits, and values exactly at the boundaries.

1. Clarify requirements and edge cases

Confirm the exact behavior for leading whitespace, optional sign, non-digit characters, and overflow. Ask about empty strings, strings with only whitespace, and sign characters without digits.

2. Design the algorithm

Plan a single-pass approach: skip leading whitespace, parse optional sign, then process digits while checking for overflow before each update. Use a 64-bit accumulator or pre-check to avoid overflow.

3. Implement with overflow handling

Write code that iterates through the string, updates the result, and clamps to INT_MIN or INT_MAX if overflow is detected. Ensure the sign is applied correctly.

4. Test with edge cases

Walk through test cases: empty string, whitespace only, '+', '-', '+-2', ' -42', '4193 with words', '2147483647', '2147483648', '-2147483648', '-2147483649'.

5. Analyze complexity and trade-offs

State that the time complexity is O(n) and space is O(1). Discuss trade-offs between using 64-bit accumulator vs. pre-checking overflow, and mention that clamping is preferred over undefined behavior.

Key Points to Mention

Leading whitespace: skip all whitespace characters until the first non-whitespace.
Optional sign: handle '+' or '-' as the first non-whitespace character.
Non-digit terminator: stop parsing at the first non-digit character.
Overflow handling: clamp to INT_MIN (-2^31) or INT_MAX (2^31 - 1) if the value exceeds the range.
Use of 64-bit accumulator or pre-check to detect overflow before it occurs.
Time and space complexity: O(n) time, O(1) space.

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