Senior Software Engineer, Machine Learning, Google Research

Google

Given n pairs of parentheses, what is the total number of different, valid combinations of those parenthesis? For example: For n = 1, the only valid combination is (), so the answer is 1. For n = 2, the valid combinations are ()() and (()), so the answer is 2. For n = 3, the valid combinations are ((())), (()()), (())(), ()(()), and ()()(), so the answer is 5. Calculate the number of valid parenthesis combinations for a given n. Explain the formula or method used to arrive at the answer. What is the underlying mathematical concept at play here, and how does it ensure that we only count valid combinations, avoiding invalid ones such as )()(? Detail the relationship between this problem and Catalan numbers, and discuss how this relationship can be utilized to efficiently compute the number of valid combinations, even for relatively large values of n.

Google

Let's design a rate limiter. This is a crucial component in many systems to prevent abuse and ensure fair usage. Your rate limiter should meet these requirements: Functionality: It should limit the number of requests a user can make within a specific time window. For example, allow a user to make 10 requests per minute. Scalability: The rate limiter needs to handle a large number of users and requests concurrently. Imagine millions of users accessing the system. Accuracy: It should accurately track and enforce the rate limits. A small degree of error is acceptable, but significant deviations are not. Low Latency: The rate limiter must not introduce significant delays in request processing. The overhead should be minimal. Fault Tolerance: The system should continue to function correctly even if some components fail. It should be resilient to outages. Cost-Effectiveness: The solution should be cost-effective in terms of resources used (e.g., memory, CPU, network bandwidth). Consider these scenarios and constraints: Users are identified by a unique ID. The time window is configurable (e.g., seconds, minutes, hours). The rate limit is also configurable per user or group of users. You can use any data structures and algorithms you deem appropriate. Assume you have access to a distributed cache (e.g., Redis, Memcached). Walk me through your design. Discuss different approaches, their trade-offs, and how you would address the requirements. Specifically, consider the following: Data structures for storing request counts. Algorithms for incrementing and checking request counts. Handling concurrency and race conditions. Strategies for distributing the rate limiter across multiple servers. How to handle exceeding the rate limit (e.g., returning an error code). Monitoring and alerting. For example, if a user with ID user123 tries to make 11 requests within a minute when their limit is 10, the rate limiter should reject the 11th request. How would your system achieve this efficiently and reliably at scale?

Google

Can you describe a time you had to work with a difficult team member and how you handled the situation? This is a common behavioral interview question designed to assess your interpersonal skills, conflict resolution abilities, and ability to work effectively in a team environment, even when faced with challenges. When answering this question, it's crucial to provide a specific example, detailing the situation, your actions, and the resulting outcome. This allows the interviewer to understand your approach and evaluate your effectiveness. For instance, you might discuss a project where a team member consistently missed deadlines, hindering the team's progress. In your response, you should: Describe the Situation: Clearly outline the project, the team member's role, and the specific behaviors that made them difficult to work with (e.g., missed deadlines, lack of communication, negative attitude). Be objective and avoid accusatory language. Explain Your Actions: Detail the steps you took to address the situation. Did you have a one-on-one conversation with the team member? Did you involve a supervisor or mentor? Did you try to understand the reasons behind their behavior? Did you adjust your own approach to accommodate their needs? Highlight the Result: Explain the outcome of your actions. Were you able to resolve the issue? Did the team member improve their performance? What did you learn from the experience? Even if the outcome wasn't ideal, focus on the lessons learned and how you would approach a similar situation in the future. Remember, the STAR method (Situation, Task, Action, Result) can be a helpful framework for structuring your answer. The interviewer wants to see that you can navigate challenging interpersonal dynamics professionally and contribute to a positive team environment.