The flat case I got pretty quickly, just scan for the pattern and replace.
Use a stack-based approach to handle nested parentheses and repeat counts. Iterate through the string, pushing current string and repeat count onto stacks when encountering '(', and popping and expanding when encountering ')'. This naturally handles nesting and ensures linear time complexity.
Pro tip: Clarify edge cases upfront (e.g., empty strings, invalid input, multi-digit repeat counts) and discuss time/space complexity. Mention that a recursive descent parser is an alternative, but the stack approach is more efficient and avoids recursion depth issues.
Restate the problem to ensure clarity, and ask clarifying questions about input format, valid characters, and expected behavior for edge cases like empty strings or invalid patterns.
Decide between a stack-based iterative solution or recursion. Explain why a stack is suitable for handling nested structures and avoids potential stack overflow.
Describe the step-by-step process: initialize stacks for strings and counts, iterate through characters, handle '(', ')', '{', '}', and regular characters, and build the result incrementally.
State the time and space complexity (O(n) time, O(n) space in worst case) and walk through an example to verify correctness, including nested cases.
Mention potential optimizations like using a single stack with a custom object, or a recursive approach, and discuss trade-offs.
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