Design a search index similar to twitter search

Sending user notifications is a common requirement in system design. Design a notification service for an organization. The system will use shared services for the underlying messaging implementation (email, sms, push notifications, etc) so the actual messaging implementation does not need to be designed. The system should support a user publishing a notification to a single user or groups of users. Notifications can be triggered manually via a web UI or programmatically via an API. Users should be able to view their past notifications they published. If a user is unable to receive a notification, they should still receive it at the next opportunity and not miss the message. The notification service should scale to billions of notifications per day, with messages delivered within a few seconds, with five 9s uptime.

Design an app like google maps. The app should provide the quickest possible route between two arbitrary locations. It should provide an ETA, estimated time to reach a destination, using current traffic data.

Functional Requirements:

1. Users can upload videos

2. Users can view videos

3. Search videos by video title

4. Videos should have like and view counts

5. Users can comment on videos

Design a reservation and payment system for a parking garage. Functional requirements include "spot booking", the ability to make payments, prevent booking the same parking spot, different classes of parking spots (compact,regular,large vehicles, handicap) with different prices. The non functional requirements include high consistency and availability.