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Molocoads·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Interviewed for a software engineer role at Molocoads and got a string parsing problem that looked deceptively clean on the surface. Not a ton of context about the broader process, just this one problem to work through.

Questions Asked (1)

Q1

Given a valid parentheses string, compute its score where '()' equals 1, adjacent strings add their scores, and a string wrapped in outer parentheses doubles its inner score.

Algorithms & Data Structures
Author's notes

I knew this was a stack problem pretty quickly but fumbled the doubling logic for nested cases.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and walking through a simple example to confirm understanding. Then present a stack-based solution that processes the string character by character, maintaining a stack of scores for each nesting level. Finally, discuss time and space complexity and consider edge cases.

Pro tip: Mention that the score can also be computed by tracking depth: each '()' contributes 2^depth to the total score, which is a simpler O(1) space solution. This shows you can think beyond the obvious stack approach.

1. Clarify and Confirm

Restate the problem in your own words and ask clarifying questions about input constraints, expected output, and edge cases. Confirm the scoring rules with a simple example like '()()' = 2 and '(())' = 2.

2. Choose an Approach

Decide between a stack-based simulation and a depth-based mathematical approach. Explain the trade-offs: stack is intuitive and directly follows the rules, while depth-based is more space-efficient.

3. Walk Through the Algorithm

For the stack approach: initialize a stack with [0], iterate through the string; on '(' push 0, on ')' pop the top, double it (or set to 1 if it was 0), and add to the new top. For the depth approach: maintain depth, increment on '(', decrement on ')', and when encountering '()', add 2^depth to the total.

4. Analyze Complexity

State that both approaches run in O(n) time. The stack approach uses O(n) space in the worst case (e.g., deeply nested), while the depth approach uses O(1) extra space.

5. Test with Examples

Run through provided examples and edge cases like empty string, '()', '(())', '()()', and '(()(()))' to verify correctness. Discuss potential pitfalls such as integer overflow if scores can be large.

Key Points to Mention

  • Stack data structure for tracking nested scores
  • Depth-based mathematical insight: score contribution of each '()' is 2^depth
  • Time complexity O(n) and space complexity O(n) for stack, O(1) for depth approach
  • Handling of adjacent and nested parentheses according to rules
  • Edge cases: empty string, single pair, deeply nested, multiple adjacent pairs
  • Potential integer overflow and use of appropriate data types

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