G
27Challenges
3War Rooms
~42hPrep Time
4/27Completed
Structured problem-solving at scale. Expect ambiguity, depth, and systems thinking.
15% complete
Interview rounds:Phone ScreenCoding ×2System DesignBehavioral (Googleyness)
DSA3
Datacenter Network Partitions (Matrix DFS)Our datacenter is represented as a 2D grid. `1` represents an active server rack, `0` repr…
Mid~30 min
Optimal Server Rack Cooling (Two Pointers)Given an array of server rack heights, choose two racks such that, combined with the floor…
Mid~30 min
Visible Security Cameras (Binary Tree Right Side View)Given the `root` of a binary tree, imagine yourself standing on the right side of it, retu…
Mid~30 min
War Room3
gRPC Deadline Propagation Causing Cascading TimeoutService A calls Service B (gRPC, 500ms deadline). Service B calls Service C (no deadline s…
Senior~25 min
SLO Budget Burned by a Single Chatty ClientYour API has a 99.9% SLO. Datadog shows your error rate spiked to 5% for the past 3 hours …
Mid~20 min
Istio mTLS Breaks Service After Policy ChangeYour security team changed the Istio PeerAuthentication policy from PERMISSIVE to STRICT a…
Senior~25 min
System Design14
Design a URL Shortener (Bitly)Design a system that takes long URLs and generates 7-character short links. It must handle…
Mid~45 min
Design Google Search AutocompleteDesign an autocomplete system that returns the top-5 suggestions for any prefix in under 5…
Senior~45 min
Design a Web CrawlerCrawl 1 billion web pages a month to train an LLM. Avoid crawling the same page twice, res…
Senior~60 min
Design a Key-Value Store (Redis)Design a distributed key-value store that supports GET, PUT, DELETE with sub-millisecond l…
Mid~50 min
Design Dropbox (File Sync)Design a file synchronization service like Dropbox. Users upload files from desktop client…
Mid~55 min
Design Google Maps (Routing)Design the routing backend for a maps application. Given an origin and destination, comput…
Senior~60 min
Design Google Docs (Real-Time Collaboration)Design a real-time collaborative document editor like Google Docs. Multiple users can edit…
Senior~60 min
Design a Distributed Lock ServiceDesign a distributed lock service (like Google Chubby or Apache ZooKeeper). Allow multiple…
Senior~50 min
Design an Ad Click Aggregation SystemDesign a system to count ad clicks for billing and analytics. Ad networks must know clicks…
Senior~55 min
Design an Email Service (Gmail)Design a large-scale email service supporting 1B+ users. Support sending, receiving, threa…
Senior~55 min
Design a DNS SystemDesign the Domain Name System — the internet's distributed directory that translates domai…
Senior~50 min
Design a Pub/Sub SystemDesign a publish-subscribe messaging system. Publishers send messages to topics without kn…
Mid~40 min
Design a Distributed File System (GFS/HDFS)Design Google File System (GFS). Store exabytes of data across thousands of commodity mach…
Senior~60 min
Design a Search Engine (Inverted Index)Design a full-text search engine that indexes 50 billion web pages and returns results for…
Senior~60 min
Tech Debt Tribunal4
Fix Mutable Shared StateHttpClient mutates the global config timeout to 50ms. AnalyticsClient reads the same objec…
Mid~25 min
No Graceful Shutdown — In-Flight Requests KilledWhen Kubernetes sends SIGTERM, the Node.js server exits immediately — killing all in-fligh…
Senior~30 min
String Template Literals Over Array JoinAn email template builder concatenates 50+ lines with string interpolation in a loop, crea…
Junior~15 min
Console.log Left in Production BuildThe production bundle contains 47 console.log calls including raw user data, JWT payloads,…
Junior~15 min
War RoomGoogle-specific3
Bigtable Replication LagA Bigtable replication lag is causing search staleness for 3% of queries. Reads are return…
P1+1200 XP
Spanner Deadlock CascadeCloud Spanner transaction deadlocks are cascading across the Ads serving pipeline. CPC bid…
P0+1500 XP
Pub/Sub Consumer LagA Pub/Sub subscription has a 12-hour backlog. Downstream analytics pipelines are producing…
P2+900 XP