Offensive Security Engineer, Red Team X

Meta

You are given a binary tree. Write a function to flatten the binary tree into a linked list in-place. The linked list should be in the same order as a pre-order traversal of the binary tree. This means that for each node, the right pointer should point to the next node in the pre-order traversal, and the left pointer should be null. For example, consider the following binary tree: 1 / 2 5 / 3 4 6 After flattening, the tree should look like this: 1 -> 2 -> 3 -> 4 -> 5 -> 6 Each node's right pointer points to the next node in the pre-order traversal, and all left pointers are null. Clarifications: The function should modify the tree in-place. The pre-order traversal should be followed. The left pointers of all nodes should be set to null after flattening. Could you provide an efficient algorithm to accomplish this, and what is the time and space complexity of your solution?

Meta

Let's design a new feature for the Facebook app: Ephemeral Groups. These groups function like regular Facebook groups but with a key difference: all content (posts, comments, media) within the group is automatically deleted after 24 hours. The group itself remains, but the content vanishes. Imagine users creating groups for flash events, temporary project collaborations, or just sharing memes that are only funny for a day. Here are some considerations to guide our design: Use Cases: What are the primary use cases for Ephemeral Groups? Consider examples beyond those mentioned above. User Interface: How would users create and identify Ephemeral Groups within the existing Facebook app? How is it visually distinct? Data Storage: How would you efficiently store and automatically delete content to minimize storage costs and ensure compliance with the 24-hour expiration? Abuse Prevention: How do you prevent the misuse of Ephemeral Groups for sharing harmful or illegal content, given the disappearing nature of the data? Notifications: How would notifications work for Ephemeral Groups? Should users receive notifications for content that will disappear soon? Privacy: How would we make users aware of the ephemeral nature of the group and its content to manage their privacy expectations effectively? Scalability: How would this feature scale to handle potentially millions of Ephemeral Groups without impacting the performance of the overall Facebook platform? Walk me through your design proposal, addressing these considerations and any other relevant aspects you believe are important.

Meta

Could you describe a situation where you faced a significant memory leak issue in a C++ application and how you diagnosed and resolved it? Please walk me through the tools and techniques you used, the challenges you encountered, and the ultimate solution you implemented. For example, imagine you're working on a large-scale C++ application for processing high-volume financial transactions. The application is experiencing performance degradation over time, eventually leading to crashes. After initial investigation, you suspect a memory leak. Describe your approach to identifying the source of the leak. Consider discussing the specific tools you might employ, such as memory profilers (e.g., Valgrind, AddressSanitizer), debugging techniques (e.g., heap analysis), and code review strategies. What were some of the initial hypotheses you formed, and how did you validate or refute them? What were the key code areas you focused on based on your initial findings? Furthermore, explain any specific coding practices or patterns that contributed to the leak (e.g., improper use of smart pointers, forgetting to release dynamically allocated memory). How did you correct these issues, and what steps did you take to prevent similar leaks from occurring in the future? Did you implement any automated testing or monitoring to detect memory leaks early on? Finally, reflect on any lessons learned from this experience and how it has shaped your approach to memory management in C++.