Uber Mobile Engineer System Design Questions

With many Uber users dependent on the app in low connectivity areas, designing an Offline-First Sync Engine is critical. As a Mobile Engineer, your task is to create a robust class to manage local data persistence and synchronization with the server.
Problem statement: Define a class OfflineSyncEngine that maintains local copies of user ride requests and syncs them with a remote server when connectivity is restored.
- addRideRequest(ride: RideRequest) -> None: Adds a ride request to the local queue.
- syncWithServer() -> None: Syncs all local requests with the server when a connection is available.
Example 1:
Input: syncEngine.addRideRequest(RideRequest(userId='user1', origin='A', destination='B'))
Output: None
Explanation: The ride request is stored locally until a connection is established.
Example 2:
Input: syncEngine.syncWithServer()
Output: None
Explanation: Syncs the local ride requests with the server.
Constraints:
- The system should handle up to 500 requests locally.
- Data types for trip requests must be validated.

Uber needs an effective Notifications Center to manage ride updates, promotions, and driver messages in real-time. As a Mobile Engineer, you will design a system that handles notifications through multiple channels.
Problem statement: Define the NotificationCenter class, which must manage sending and storing notifications for users. You should implement methods to send notifications via different channels and to retrieve pending notifications.
- sendNotification(userId: string, message: string, channel: string) -> None: Sends a notification to the intended user through the specified channel (e.g., SMS, push).
- getPendingNotifications(userId: string) -> List[str]: Retrieves and returns all pending notifications for the given user.
Example 1:
Input: notificationCenter.sendNotification('user1', 'Your ride is arriving!', 'push')
Output: None
Explanation: Successfully sends a push notification.
Example 2:
Input: notificationCenter.getPendingNotifications('user1')
Output: ['Your ride is arriving!']
Explanation: Retrieves the pending notification message for the user.
Constraints:
- The number of notifications should not exceed 1000 per user.
- User ID and message should be non-empty strings.