My first instinct was recursion but I fumbled explaining it out loud.
Use a stack to handle nested encoded strings, pushing characters and numbers as you parse, and popping when you encounter a closing bracket to build the decoded substring. Alternatively, use recursion to process each bracket pair, which naturally handles nesting. Discuss trade-offs between iterative and recursive approaches, and analyze time and space complexity.
Pro tip: Clarify constraints upfront (e.g., input validity, digit handling, character set) to avoid edge-case pitfalls, and mention that you'd write unit tests for cases like nested brackets, multi-digit numbers, and empty strings.
Restate the problem in your own words, ask clarifying questions about input format, validity, and edge cases (e.g., nested brackets, multi-digit counts, empty strings).
Decide between stack-based iterative parsing or recursive descent. Explain why one might be preferable (e.g., stack avoids recursion depth limits).
Trace your algorithm on a sample like '3[a]2[bc]' or a nested case like '2[abc]3[cd]ef' to demonstrate correctness and handling of nesting.
State time and space complexity (O(n) time, O(n) space for stack) and discuss edge cases such as multi-digit numbers, adjacent brackets, and invalid input.
Write clean code with meaningful variable names, then mentally test or suggest test cases to verify the solution.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.