Practice/Amazon/Design Threads App

Design Threads App

Object Oriented DesignMust

Problem

Design and implement a social media feed system where users can follow each other and view posts from people they follow. The system should support creating users, establishing follow relationships, creating posts, and generating personalized feeds.

Your implementation should handle the core operations of a social network: user management, follow/unfollow functionality, post creation, and feed generation. The feed should display posts from followed users in reverse chronological order (most recent first).

Requirements

1. User Management: Create and manage user accounts with unique identifiers
2. Follow System: Allow users to follow and unfollow other users
3. Post Creation: Users can create posts with text content
4. Feed Generation: Generate a personalized feed showing posts from followed users
5. Chronological Ordering: Posts in the feed should be ordered by timestamp (newest first)
6. Feed Limit: Support limiting the number of posts returned in a feed

Constraints

• User IDs and usernames are unique strings
• Post content is a non-empty string (max length: 280 characters)
• A user cannot follow themselves
• Following the same user multiple times has no additional effect
• Feed should return at most limit posts (default: 10)
• Timestamps should be monotonically increasing for ordering purposes
• System should handle at least 10,000 users and 100,000 posts efficiently

Examples

Example 1: Basic Follow and Feed

system = SocialFeedSystem() system.create_user("u1", "alice") system.create_user("u2", "bob") system.follow("u1", "u2") // Alice follows Bob system.create_post("u2", "Hello from Bob!") feed = system.get_feed("u1") // Returns: [Post(author="u2", content="Hello from Bob!")]

Example 2: Multiple Follows

system = SocialFeedSystem() system.create_user("u1", "alice") system.create_user("u2", "bob") system.create_user("u3", "charlie") system.follow("u1", "u2") system.follow("u1", "u3") system.create_post("u2", "Post from Bob") system.create_post("u3", "Post from Charlie") feed = system.get_feed("u1") // Returns posts from both Bob and Charlie, ordered by timestamp

Example 3: Unfollow

system = SocialFeedSystem() system.create_user("u1", "alice") system.create_user("u2", "bob") system.follow("u1", "u2") system.create_post("u2", "Message 1") system.unfollow("u1", "u2") feed = system.get_feed("u1") // Returns: [] (empty feed after unfollowing)