My first instinct was recursion and it mostly worked, but I fumbled on parsing the number inside the braces when it had two digits.
Clarify the grammar and edge cases first, then propose a stack-based solution that processes characters sequentially, using a stack to handle nested repetitions. Discuss time and space complexity, and consider trade-offs between iterative and recursive approaches.
Pro tip: Mention that you would use a stack of frames storing the current string and repetition count, and that you can optimize by only pushing when encountering a brace or digit, avoiding unnecessary stack operations.
Ask about input constraints: allowed characters, maximum nesting depth, whether repetition counts can be multi-digit, and if malformed inputs need handling. Confirm expected output for examples.
Propose a stack-based approach: iterate through the string, maintaining a current string and a stack of (previous string, repetition count) frames. On '(', push current state and reset; on ')', pop and repeat; on '{', parse the number; on other characters, append to current string.
State that time complexity is O(n * max repetition) or O(output length) and space is O(output length) due to string building. Compare with recursive descent parsing, noting stack overflow risks for deep nesting.
Write clean code with meaningful variable names, handling multi-digit numbers and nested structures. Walk through the given example step-by-step to verify correctness.
Mention potential optimizations like using a StringBuilder or list of characters to avoid string concatenation overhead, and how to handle malformed inputs or additional features like escaping.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.