Data Engineer, Alexa Enterprise Data

Amazon

You are given a string moves of length n consisting only of characters 'L', 'R', and '_'. The string represents your movement on a number line starting from the origin 0. In the ith move, you can choose one of the following directions: move to the left if moves[i] = 'L' or moves[i] = '_' move to the right if moves[i] = 'R' or moves[i] = '_' Return the *distance from the origin* of the *furthest* point you can get to after n moves. Example 1: Input: moves = L_RL__R Output: 3 Explanation: The furthest point we can reach from the origin 0 is point -3 through the following sequence of moves LLRLLLR. Example 2: Input: moves = R__LL Output: 5 Explanation: The furthest point we can reach from the origin 0 is point -5 through the following sequence of moves LRLLLLL. Example 3: Input: moves = _ Output: 7 Explanation: The furthest point we can reach from the origin 0 is point 7 through the following sequence of moves RRRRRRR.

Amazon

Let's delve into the fascinating world of operating systems. Imagine you're designing a new OS, and you need to implement a memory management system. Discuss the following: Virtual Memory: Explain the concept of virtual memory. How does it help in managing memory efficiently, especially when dealing with processes that require more memory than physically available? Provide a specific example of a scenario where virtual memory shines, such as running multiple large applications concurrently on a system with limited RAM. What are the benefits and drawbacks of using virtual memory? Specifically discuss the performance overhead associated with page faults. Page Replacement Algorithms: Describe different page replacement algorithms (e.g., FIFO, LRU, Optimal). For each algorithm, provide a step-by-step example using a reference string of page accesses (e.g., 1, 2, 3, 4, 1, 2, 5, 1, 2, 3). Calculate the number of page faults for each algorithm. Discuss the trade-offs between the complexity of the algorithm and its performance in terms of minimizing page faults. Explain a situation where FIFO would perform worse than LRU, and vice versa. Memory Fragmentation: Explain internal and external fragmentation. Give examples for each. What are the causes of each type of fragmentation? What strategies can be used to mitigate memory fragmentation (e.g., compaction, paging, segmentation)? Discuss the advantages and disadvantages of each strategy. Protection and Security: How does the OS protect memory from unauthorized access by different processes? Explain the role of memory protection mechanisms like base and limit registers, and page table entries (PTEs) with protection bits. Describe a scenario where a process attempts to access memory outside of its allocated region, and explain how the OS would handle this situation to prevent security breaches. How can techniques like Address Space Layout Randomization (ASLR) further enhance memory security?

Amazon

Tell me about a project that you're most proud of. To help me understand the scope and impact, please provide specific details about the project, including: The problem: What challenge were you trying to solve, and why was it important? Your role: What specific responsibilities did you have on the project? What were your key contributions? The technical details: What technologies, tools, or techniques did you use? For example, did you work with a specific programming language, framework, or database? The outcome: What were the results of the project? Did you meet the initial goals? Did you encounter any unexpected benefits or challenges? What did you learn?: Looking back, what would you do differently? What skills or knowledge did you gain from the experience? Did you face any setbacks, and how did you overcome them? For instance, if you worked on a project to improve the performance of a web application, you might discuss the specific performance bottlenecks you identified, the optimization techniques you implemented (e.g., caching, code optimization), and the resulting improvement in response time or throughput. Or, if you designed a new feature for a mobile app, you could describe the user research you conducted, the design process you followed, and the metrics you used to measure the feature's success. Be prepared to discuss technical challenges you faced and how you addressed them.