Google Backend Engineer System Design Questions

Google Chat requires a reliable messaging system to handle messages between users effectively. A simple message queue can be implemented to ensure that messages are processed in the order they are received.
Problem Statement: Design a MessageQueue class that allows enqueuing and dequeuing messages, ensuring that all messages are processed in FIFO order.
Class Signature: class MessageQueue:
- def __init__(self): — initializes the message queue.
- def enqueue(self, message: str) -> None: — adds a message to the queue.
- def dequeue(self) -> str: — removes and returns the oldest message from the queue. If the queue is empty, raises an exception.
Example 1:
Input: msg_queue = MessageQueue(); msg_queue.enqueue('Hello'); msg_queue.enqueue('World'); msg_queue.dequeue()
Output: 'Hello'
Constraints:
- The message length is at most 10^5 characters.

As Google Cloud offers APIs to developers, it's essential to manage the rate of requests to prevent abuse. A rate limiter needs to enforce a maximum number of requests per time frame.
Problem Statement: Design a RateLimiter class which limits the number of API requests per second.
Class Signature: class RateLimiter:
- def __init__(self, requests_per_second: int): — initializes the rate limiter with the specified maximum requests per second.
- def allow_request(self, user_id: str) -> bool: — returns True if the request is allowed according to the rate limit, otherwise False.
- def reset(self, user_id: str) -> None: — resets the request count for a specific user.
Example 1:
Input: RateLimiter(2); rate_limiter.allow_request('user1')
Output: True
Input: rate_limiter.allow_request('user1')
Output: True
Input: rate_limiter.allow_request('user1')
Output: False
Input: rate_limiter.reset('user1')
Constraints:
- 1 <= requests_per_second <= 100
- A user can make at least one request.