Start by clarifying the requirements and edge cases, then outline a step-by-step parsing strategy that handles '::' expansion and embedded IPv4. Emphasize validation rules and propose a clean implementation with clear separation of concerns.
Pro tip: Mention that you would use a state machine or regex for initial validation, but ultimately rely on manual parsing for full control and performance. Also, discuss how you would test with edge cases like multiple '::', invalid groups, and IPv4-mapped addresses.
Ask about input constraints, expected output format, and how to handle invalid inputs. Confirm whether to support IPv4-mapped addresses and zone IDs.
Outline steps: split on '::' to handle shorthand, then split each part on ':' to get groups. Validate each group as hex (1-4 digits) and handle embedded IPv4 in the last 32 bits.
For each group, strip leading zeros and pad to 4 digits. For '::', calculate the number of missing groups and insert zeros. For IPv4, convert to two hex groups.
Check for multiple '::', invalid characters, too many/few groups, and invalid IPv4. Return an error or throw an exception as appropriate.
Write unit tests covering valid and invalid cases. Discuss time/space complexity (O(n)) and potential optimizations like avoiding regex for performance.
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