← Bloomberg Interview Insights
I got the basic idea pretty fast, stack of (count, string) pairs, push on '[', pop and expand on ']'.
Use a stack-based approach to handle nested brackets: push the current string and multiplier when encountering '[', and pop and combine when encountering ']'. Alternatively, use recursion to process each bracket level. Clearly explain the algorithm, then analyze time and space complexity.
Pro tip: Mention that the stack approach naturally handles arbitrary nesting and avoids recursion depth limits, which is important for production systems. Also, discuss how you would handle edge cases like multi-digit numbers and empty strings.
Ask about input constraints: can numbers be multi-digit? Are there nested brackets? What about invalid inputs? This shows thoroughness.
Decide between stack-based iterative and recursive solutions. Explain why stack is often preferred for its simplicity and avoidance of recursion limits.
Describe step-by-step how to parse the string, using a stack to store previous strings and repeat counts, and building the result incrementally.
State that time complexity is O(n) where n is the length of the decoded string (or O(m) where m is input length if considering output size), and space complexity is O(n) for the stack and result.
Trace through the given example '3[a2[c]]' to verify correctness, and mention additional test cases like '2[abc]3[cd]ef' or '10[a]'.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.