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Seems trivial until you start thinking about edge cases like leap years, different month lengths, same-day input.
Clarify the input format and edge cases (e.g., date order, time zones, leap years) before coding. Then present a clean algorithm that converts each date to a day count (e.g., days since epoch) and returns the absolute difference, handling leap years correctly. Discuss trade-offs between manual calculation and using built-in date libraries.
Pro tip: Mention that in production code you'd use a battle-tested date library (like java.time or Python's datetime) to avoid subtle bugs, but here you'll demonstrate the underlying logic to show you understand the mechanics.
Ask about input format (strings, date objects), whether dates can be in any order, time zones, and if the difference should be inclusive/exclusive. Confirm handling of leap years and invalid dates.
Decide between using a built-in library or implementing from scratch. For interviews, implementing from scratch is often expected; explain that you'll convert each date to a serial day number.
Outline steps: parse the date into year, month, day; compute days from a fixed epoch (e.g., 0001-01-01) using a formula that accounts for leap years; then return the absolute difference.
Write clean code with helper functions for leap year check and days-before-month. Test with cases like same date, consecutive days, leap year boundaries, and reversed order.
State that the algorithm runs in O(1) time and space. Mention that using a library would be more robust in production, and discuss potential pitfalls like time zones.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.