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Vercel

Hard
14Challenges
1War Rooms
~18hPrep Time
2/14Completed

Elite DX engineers. Edge runtimes, build performance, and developer empathy.

14% complete
Interview rounds:Take-Home ProjectTechnical ReviewSystem DesignCulture

DSA4

CI/CD Pipeline Dependency Resolution (Graphs)Our monorepo build system fails because packages depend on each other. Given packages and …
Mid~40 min
AWS Lambda Job Packing (DP / Knapsack)We rent AWS Lambda instances with a maximum RAM capacity of M MB. We have a queue of backg…
Senior~45 min
Dynamic API Routing (Trie)You are writing the core router for a new web framework. You need to support fast path mat…
Senior~50 min
UI Component Tree ReconstructionGiven two integer arrays `preorder` and `inorder` where `preorder` is the preorder travers…
Senior~50 min

PR Review3

React useEffect Infinite LoopA junior dev reorganised the data-fetch logic inside a React component. QA reports the bro…
Junior~10 min
Sequential Awaits — N×1 Second Dashboard LoadThe dashboard API endpoint takes ~3 seconds to respond after a junior dev added two additi…
Junior~10 min
Heavy Computation Blocking the Event LoopA new feature allows admins to download an audit log of 100,000+ records. The file generat…
Mid~12 min

War Room2

502 Bad Gateway LoopNginx is throwing 502 Bad Gateway errors. You check the Node.js application server, and it…
Junior~15 min
Let's Encrypt Rate Limit Blocks Certificate RenewalYour platform provisions Let's Encrypt certificates automatically for customer custom doma…
Junior~20 min

System Design1

Design a Code Deployment System (CI/CD)Design a CI/CD system that automatically builds, tests, and deploys code on every git push…
Senior~50 min

Tech Debt Tribunal3

Synchronous File I/O Blocking the Event LoopA Node.js API reads a config file using fs.readFileSync() on every request. Under 200 conc…
Junior~20 min
useEffect with Missing Dependency ArrayA React component uses useEffect with an empty dependency array but references props and s…
Junior~20 min
Global Variables in Node.js ModuleA request counter and session store are stored as module-level globals. In a multi-instanc…
Junior~20 min

War RoomVercel-specific1

Edge Function Cold Start SpikeA Vercel Edge Function deployment triggered a cold start spike across 12 PoP locations. P9…
P1+1100 XP