Seemed trivial at first and I almost wrote a one-liner without thinking about the 'group' part.
Clarify the exact transformation: each period is replaced by an exclamation mark, and then an additional exclamation mark is appended after each such group. Walk through a concrete example to confirm understanding, then implement a straightforward string replacement followed by appending an extra exclamation mark after each replaced group. Discuss edge cases and test your solution.
Pro tip: Before coding, confirm with the interviewer whether consecutive periods should be treated as separate groups or as a single group, as this ambiguity can significantly affect the implementation. Also, mention that you would write unit tests to cover edge cases like empty strings, no periods, and multiple periods.
Ask the interviewer to confirm the transformation: replace each period with an exclamation mark, then append an additional exclamation mark after each such group. Clarify how consecutive periods should be handled.
Take a sample string like 'Hello. World.' and manually apply the transformation to ensure you understand the expected output. This will help you catch any misinterpretations early.
Decide on a simple approach: iterate through the string, build a new string, and whenever you encounter a period, append '!!' to the result. Otherwise, append the current character.
Write clean code with meaningful variable names. Test with edge cases: empty string, string with no periods, string with multiple consecutive periods, and string starting or ending with a period.
State the time and space complexity (O(n) time, O(n) space for the new string). Mention potential optimizations like using a StringBuilder or equivalent for efficiency in languages like Java or C#.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.