Support Engineer - Incident Management, AWS Incident Response (AIR)

Amazon

Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself). For example: If the tree is [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1, then the expected output is 3, because the LCA of nodes 5 and 1 is 3. If the tree is [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4, then the expected output is 5, because the LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition. If the tree is [1,2], p = 1, q = 2, then the expected output is 1. Consider these constraints: The number of nodes in the tree is in the range [2, 10^5]. -10^9 <= Node.val <= 10^9 All Node.val are unique. p != q p and q will exist in the tree.

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

Describe a time when a plan did not go as expected.