Systems QA Engineer

Apple

Given an integer n, return the count of all numbers with unique digits, x, where 0 <= x < 10^n. For example: Input: n = 2 Output: 91 Explanation: The answer should be the total numbers in the range of 0 <= x < 100, excluding 11,22,33,44,55,66,77,88,99 Input: n = 0 Output: 1

Apple

Let's talk about semaphores. Could you please explain what semaphores are, and how they are used in operating systems or concurrent programming? Provide examples of situations where semaphores are useful for controlling access to shared resources. Explain the difference between binary and counting semaphores. Furthermore, can you discuss potential problems that can arise when using semaphores, such as deadlocks or starvation, and how these problems can be addressed? For instance, consider a scenario where multiple threads need to access a database connection pool. How can semaphores be employed to manage access to the limited number of connections in the pool, preventing overuse and ensuring fair allocation among threads?

Apple

Let's discuss your approach to debugging malfunctions. Imagine you are on call for a critical e-commerce platform, and users start reporting that they are unable to complete their purchases. The error logs show a vague Transaction Failed message with no clear indication of the root cause. The customer service team is overwhelmed with complaints, and the business is losing revenue every minute the issue persists. Describe your initial steps in diagnosing the problem.** What tools or techniques would you use to gather more information? Would you focus on the front-end, back-end, or both? How would you prioritize your debugging efforts?** Would you start by examining the most recent code changes, monitoring server resources, or checking database connections? Explain your strategy for isolating the fault.** What methods would you employ to narrow down the potential causes of the malfunction, such as bisecting the code, using debugging tools, or performing hypothesis testing? Outline your approach to resolving the issue.** Once you have identified the root cause, what steps would you take to fix it quickly and effectively? How would you ensure that your fix does not introduce new problems? Discuss how you would prevent similar malfunctions from occurring in the future.** What proactive measures would you implement to improve the platform's reliability and resilience, such as adding better logging, implementing automated testing, or improving monitoring? Walk me through your thought process and provide specific examples of how you would tackle each step of the debugging process. I'm interested in hearing about your experience with similar situations and how you have successfully resolved them in the past.