Safari Core Technologies Security 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 delve into the fascinating world of computer systems. I'd like you to design a simplified operating system. Assume you're building this OS for a resource-constrained embedded system, like a smart thermostat or a simple microcontroller-based device. Your design should address the following key aspects: Memory Management: Describe your approach to memory allocation and deallocation. How would you prevent memory leaks and fragmentation in this environment? Would you use static allocation, dynamic allocation, or a combination of both? Explain your reasoning, giving specific examples of how your chosen methods would work in practice. Process/Task Scheduling: How would you schedule tasks to run on the processor? Would you opt for a preemptive or non-preemptive scheduler? What scheduling algorithm (e.g., Round Robin, Priority-based) would you use, and why? Consider the trade-offs between responsiveness, fairness, and overhead. Imagine you have three tasks: Task A (high priority, short bursts), Task B (medium priority, longer computation), and Task C (low priority, background task). How would your scheduler handle these tasks? Interrupt Handling: Explain how your OS would handle interrupts from hardware devices (e.g., a temperature sensor, a button press). How would you ensure that interrupt handlers are efficient and don't disrupt the normal operation of the system? Describe the steps involved in processing an interrupt, from the moment it occurs to the point where the interrupted task resumes execution. File System (Optional): If your embedded system requires persistent storage, outline a simple file system design. How would you organize files and directories? What data structures would you use to track file metadata (e.g., name, size, location)? How would you handle file creation, deletion, and reading/writing operations? Assume the storage medium is a small flash memory chip with limited write cycles. Inter-Process Communication (IPC): How would different tasks or processes communicate with each other within your OS? Would you use message queues, shared memory, or another mechanism? Explain the advantages and disadvantages of your chosen approach. For example, consider a scenario where one task needs to send sensor data to another task for processing. How would you implement this communication? Remember to justify your design choices based on the constraints of the embedded system, such as limited memory, processing power, and energy consumption. Aim for simplicity, efficiency, and reliability in your design. Your explanation should demonstrate a solid understanding of operating system principles and their practical application in a real-world scenario.

Apple

Let's say a developer doesn't agree that a reported bug is actually a bug. How would you handle this situation? Be specific. For example, imagine you're a QA engineer, and you find that a button on a webpage is slightly misaligned in a specific browser. You log this as a bug, but the front-end developer says it's 'within acceptable tolerances' and refuses to fix it. Or, perhaps a back-end developer claims that a specific edge-case error is so rare it's not worth the effort to address, even though you believe it violates the product's stated reliability goals. What steps would you take to resolve the disagreement while maintaining a positive working relationship and ensuring product quality? Consider the different approaches you could take based on the severity and impact of the potential bug.