iPhone System Reliability Engineer

Apple

Given an integer array nums where every element appears three times except for one, which appears exactly once. Find the single element and return it. You must implement a solution with a linear runtime complexity and use only constant extra space. For example, if the input is nums = [2,2,3,2], the output should be 3. Another example, if the input is nums = [0,1,0,1,0,1,99], the output should be 99. How do you solve this problem, considering edge cases like empty input, presence of zero, and negative numbers?

Apple

System Design Question: Designing a URL Shortening Service like TinyURL Let's design a URL shortening service like TinyURL. Consider the following: Functional Requirements: Given a long URL, the service should generate a shorter and unique alias. When users access the short URL, they should be redirected to the original long URL. The system should be highly available and reliable. Analytics: Track the number of times a short URL has been accessed. Non-Functional Requirements: The system should have low latency for URL redirection. Shortened URLs should be relatively short in length. The system should be able to handle a large number of URL shortening and redirection requests. Scalability: The system should be scalable to handle a growing number of URLs and users. Capacity Estimation & Constraints: Assume 100 million URLs are shortened per day. Assume 1 billion redirections per day. Assume a read/write ratio of 10:1 (redirections vs. shortening). Short URL length should be as short as possible (e.g., 7 characters). High-Level Design: Discuss the components involved (e.g., web servers, application servers, database). Explain the URL shortening and redirection process. Propose a suitable database (e.g., SQL or NoSQL). Detailed Design: How to generate unique short URLs? Discuss approaches like hash functions, base-62 encoding, or UUIDs. What are the tradeoffs of each approach in terms of collision probability, URL length, and performance? Explain the database schema for storing the mappings between short and long URLs. Detail the caching strategy to improve redirection performance. Where should the cache be placed (e.g., client-side, CDN, in-memory cache)? What cache eviction policy should be used? Scaling and Availability: How to scale the system to handle the expected load? Discuss techniques like load balancing, database sharding, and replication. How to ensure high availability? Discuss strategies like redundancy, failover mechanisms, and monitoring. Rate Limiting: Implement rate limiting to prevent abuse (e.g., a user shortening too many URLs in a short period of time). Discuss different rate-limiting algorithms (e.g., token bucket, leaky bucket). Walk through the design process, addressing each of these points. Explain any tradeoffs you make in your design decisions. Show examples of how different technologies or architectural choices impact system performance and scalability.

Apple

Let's explore the concept of feedback amplifiers in the context of software development teams. Imagine you are leading a team working on a critical feature for a new mobile application. Communication bottlenecks and misunderstandings are starting to impact the team's velocity and morale. As a senior engineer, you recognize the need to amplify feedback loops to improve team performance. Describe what a feedback amplifier is and how it works in practice.** Provide concrete examples of how you would implement feedback amplifiers within your team. Consider different types of feedback, such as code reviews, sprint retrospectives, and individual performance reviews. Explain the benefits of using feedback amplifiers.** How can they improve code quality, reduce bugs, and increase team collaboration? Quantify the potential impact using hypothetical scenarios or past experiences. For instance, how might more frequent code reviews, coupled with automated static analysis, lead to a measurable reduction in the number of bugs discovered in production? Discuss the potential challenges and pitfalls of implementing feedback amplifiers.** What steps would you take to mitigate these risks? Think about issues like information overload, negative feedback bias, and the time investment required to implement and maintain effective feedback loops. How would you ensure that the feedback process remains constructive, fair, and actionable for all team members? Elaborate on your answer by considering specific tools or techniques you have used in the past to amplify feedback, such as using dashboards to visualize key performance indicators, conducting regular pulse surveys to gauge team sentiment, or establishing a system for tracking and resolving action items from retrospective meetings. Also, discuss how you would tailor your approach based on the size and structure of the team, as well as the specific project goals and constraints.