45+ Questions: Deep-dive into Coding, Systems, and the unique "Googliness" culture fit. All questions include detailed answers.
LFU Cache Design: LFU evicts the item that has been used the least frequently. If there's a tie in frequency, the least recently used among them is evicted.
Data Structures Required:
Map<Key, Node>: Stores key-value pairs and links to the list node.Map<Frequency, DoublyLinkedList>: Stores lists of nodes, grouped by their access frequency.min_freq: Integer tracking the minimum frequency present in the cache.Operation: On get(key) or put(key, value), the node's frequency increases. It must be moved from its current frequency list to the frequency + 1 list. If the old frequency list becomes empty and it was the min_freq, then min_freq is incremented. Eviction removes the tail of the min_freq list.
Optimal Technique: Inorder Traversal. An inorder traversal of a BST visits nodes in strictly increasing order. We can perform an iterative inorder traversal using a stack. We decrement a counter $k$ for every node visited. The moment $k$ reaches zero, we have found the element.
Complexity: Time Complexity: O(H + k), where H is the height of the tree. This is generally faster than O(N) if k is small. Follow-up: For frequent calls, augment the tree nodes with the count of nodes in their left subtree.
Technique: Prefix and Suffix Product Arrays. We need two passes:
Example: For [1, 2, 3, 4], prefix array becomes [1, 1, 2, 6]. Suffix product starts at 1, then: $6\times1=6$; $2\times4=8$; $1\times(4\times3)=12$; $1\times(4\times3\times2)=24$. Final result: [24, 12, 8, 6].
Key Challenge: Achieving low-latency routing globally.
High Availability: Use a two-tiered approach. **L4 (Network Level)** load balancing (like Maglev or equivalent Layer 4 IP forwarding) handles massive traffic volume, distributing requests based on IP/Port. **L7 (Application Level)** load balancing (HTTP headers, URL path) sits closer to the services, handling routing, SSL termination, and rate limiting.
Distribution: Use **consistent hashing** to map client requests to backend servers, minimizing cache invalidation when servers are added or removed.
Health Checks: Frequent, non-invasive health checks are crucial for quickly removing failed nodes from the distribution pool.
Focus: Demonstrating intellectual humility and data-driven courage.
S+T: The manager decided to cut the testing phase on a new API launch to meet a hard deadline (Task: ensure quality despite pressure).
A: You respectfully presented historical data showing that skipped testing had caused 10% more Sev 1 incidents. You proposed a compromise: launch with limited functionality (MVP) but maintain the necessary integration tests. You offered to work extra hours on the tests.
R: The manager agreed. The API launched on time, the core functionality was stable, and the full feature set followed one week later with zero bugs, preserving quality.
Focus: Dealing with ambiguity, proactivity, and communication.
S+T: You were tasked with "improving user login security" (too vague). (Task: define measurable goals).
A: You broke the project down. You scheduled quick 15-minute syncs with stakeholders (PM, Security) to identify key metrics (e.g., failed login attempts, successful MFA adoption rate). You defined a clear, minimal scope (MVP: MFA integration) and documented a "Decision Log" of assumptions made, sharing it with the team.
R: The documentation reduced confusion and allowed you to deliver the MVP efficiently, which was later expanded based on solid feedback, demonstrating comfort in ambiguity.
Why Google: Link your desire to work there to their **scale, innovation, and global impact**. Mention specific products (e.g., Kubernetes, TensorFlow, Quantum Computing research) and how your skills (e.g., distributed systems) align with their DNA.
Tech Excitement: This tests curiosity (a key Googliness trait). Mention something cutting-edge but relevant to the industry, like **WebAssembly (WASM)** for enabling near-native speed in browsers, or **Homomorphic Encryption** for secure cloud computation. This shows breadth of knowledge.