Problem Understanding
Restate the problem in your own words.
Design Google Calendar
Design a Google Calendar-class scheduling system: per-user calendars with one-off and recurring events (RRULE per RFC 5545), multi-attendee invites with RSVP tracking, free-busy lookups across many calendars, time-zone-aware reminders, and multi-device sync within seconds of any edit. Reads dominate (every app open hits the day / week / month grid), but the architectural surprise sits in the data model: expanding recurring events on read vs. materialising every instance, and handling exceptions to recurrences without combinatorial blow-up. Reminders turn it into a fan-out + scheduler problem too — millions of pushes can fire on a single minute boundary.
- Google CalendarThe canonical product. RFC 5545 compliant; deep integration with Gmail invites + Meet.
- Outlook / Microsoft CalendarEnterprise-heavy; same model + room-booking + Exchange Web Services.
- Apple Calendar (iCloud)Device-coupled sync; CalDAV under the hood.
- Calendly / CronScheduling-assistant layer on top of any calendar provider — focuses on the free-busy + invite-link flow.
Your task: read the problem above, then write what the system is, who uses it, the rough scale, and the headline UX expectation — in your own words. Submit for AI review when you're ready.
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