Coinbase Software Engineer System Design Questions

As Coinbase looks to integrate social features for trading, it's essential to design a system that tracks user feeds efficiently.
Problem statement: Design a class to manage a user's feed. Supports the following methods: follow(follower_id: int, followee_id: int), unfollow(follower_id: int, followee_id: int), and get_feed(user_id: int) -> List[int]. The feed should return the most recent 10 transactions from the followed users.
- Method signatures:
- def follow(follower_id: int, followee_id: int) -> None: update the following relationship.
- def unfollow(follower_id: int, followee_id: int) -> None: remove the following relationship.
- def get_feed(user_id: int) -> List[int]: return the user feed containing transaction IDs of the most recent 10 transactions from followed users.
Example 1:
Input: manager = FeedManager()
manager.follow(1, 2)
manager.follow(1, 3)
manager.get_feed(1)
Output: [x, y, z]
Constraints:
- 1 <= follower_id, followee_id <= 10^4
- Transaction history size can be up to 10^5.

In order to optimize data retrieval times and minimize database load, Coinbase requires an LRU cache to manage frequent API requests efficiently.
Problem statement: Design and implement a class that represents an LRU Cache with a fixed capacity. Supports get(key: int) -> int and put(key: int, value: int) -> void methods.
- Method signatures:
- def get(key: int) -> int: returns the value of the key if it exists or -1.
- def put(key: int, value: int) -> None: updates the value if the key exists, otherwise, adds the key-value pair to the cache. If the cache reaches its capacity, it should invalidate the least recently used item before inserting a new item.
Example 1:
Input: cache = LRUCache(2)
cache.put(1, 1)
cache.put(2, 2)
cache.get(1)
Output: 1
cache.put(3, 3)
cache.get(2)
Output: -1
Constraints:
- 1 <= capacity <= 3000
- 0 <= key, value <= 10^4.