String manipulation related

This stored label does not describe a specific operation, so the correct interview response is to ask for examples and the exact desired output. Once the contract is clear, choose a representation: direct iteration for validation, a stack for nested syntax, a frequency table for counts, two pointers for reversal or filtering, and a builder for reconstruction. Preserve a simple invariant, such as “everything before write is finalized output” or “the stack contains unmatched opening tokens.” Address null or empty input, whitespace, separators, escaping, casing, and Unicode explicitly. Avoid using costly slicing or concatenation inside the main loop unless the language guarantees sharing. Most well-scoped manipulation tasks can be made O(n) time; extra space is O(1) for read-only scans or O(n) when a rebuilt result is needed. Treat ambiguity as a requirement question, not permission to invent semantics.