Senior Staff Software Engineer, Machine Learning, Google Ads

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

Okay, let's delve into your motivations. Why are you interested in working at this company specifically? I'm looking for more than just a generic answer about seeking a new job. I want to understand what resonates with you about our company's mission, values, and the specific role you're applying for. To give you some context, consider our commitment to innovation in the field of AI, particularly our recent work on developing more ethical and transparent algorithms. Or perhaps you're drawn to our collaborative work environment, where cross-functional teams work together to solve complex problems. Maybe you admire our company's dedication to social responsibility, like our initiatives to promote STEM education in underserved communities. When answering, please be specific and show that you've done your research. For instance, you could discuss a particular project that caught your attention, how your skills and experience align with the team's needs, or how you see yourself contributing to our company's long-term goals. Avoid vague statements like I'm a hard worker or I'm a team player without providing concrete examples. Instead, focus on demonstrating a genuine interest in our company and a clear understanding of how you can make a valuable contribution. To summarize, I want to know: What specifically attracts you to our company? How do your skills and experiences align with the requirements of this role and the company's goals? What unique contributions do you believe you can make to our team and our overall mission?