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Apple·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Apple SWE interview with a Roman numerals conversion problem. Pretty classic coding question, nothing too wild, but the edge cases around the subtractive notation are where things get interesting.

Questions Asked (1)

Q1

Given a valid Roman numeral string, write a function that converts it to its integer equivalent.

Algorithms & Data Structures
Author's notes

My first instinct was just to map each character to its value and sum them up, which works for like half the cases.

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AI HintsAI Generated

Suggested Approach

First, clarify the Roman numeral rules, especially the subtractive notation (e.g., IV = 4, IX = 9). Then, propose a solution that iterates through the string, comparing each numeral to the next: if the current is less than the next, subtract it; otherwise, add it. Finally, discuss complexity and potential optimizations.

Pro tip: Mention that you can avoid a hash map by using a switch statement or a fixed-size array for faster lookups, and note that the input is guaranteed valid, so no error handling is needed. This shows attention to performance and problem constraints.

1. Clarify rules and edge cases

Confirm the Roman numeral symbols and their values, and the subtractive notation rules. Ask if the input is always valid and if there are length constraints.

2. Outline the algorithm

Explain that you'll iterate through the string, and for each character, compare its value with the next character's value. If it's smaller, subtract it; otherwise, add it.

3. Implement the solution

Write code using a mapping from Roman characters to integers. Use a loop to process each character, applying the subtractive rule. Handle the last character separately.

4. Analyze complexity

State that the time complexity is O(n) where n is the length of the string, and space complexity is O(1) since the mapping is constant size.

5. Test with examples

Walk through examples like 'III' (3), 'IV' (4), 'IX' (9), 'LVIII' (58), and 'MCMXCIV' (1994) to verify correctness.

Key Points to Mention

  • Subtractive notation: when a smaller numeral appears before a larger one, it is subtracted (e.g., IV, IX, XL, XC, CD, CM).
  • Time complexity O(n) and space complexity O(1) with a fixed-size mapping.
  • Use of a hash map or array for O(1) lookups; mention that a switch statement can be faster.
  • The input is guaranteed valid, so no need for extensive error handling.
  • Edge cases: single character, repetitive characters (e.g., III), and subtractive pairs.
  • Potential optimization: process from right to left to avoid lookahead, but left-to-right is more intuitive.

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