Learn
Problem
Write code. Hidden tests check it. Short.
Lab
A real broken machine. Fix it in the terminal.
Project
A ticket in a real repo, in VS Code. Then explain it.
Whiteboard
Answer interview questions on a board. The AI judges it.
1Find two numbers that add up to a targetarray · pairs WhiteboardDSAEasyTo do2Check if brackets are balancedstring · matching WhiteboardDSAEasyTo do3Reverse a linked listlinked-list · in-place WhiteboardDSAEasyTo do4Merge overlapping time rangesarray · intervals WhiteboardDSAMed.To do5Longest substring without repeating charactersstring · substring WhiteboardDSAMed.To do6Count the islands in a gridgrid · graph WhiteboardDSAMed.To do7Merge k sorted linked listslinked-list · sorting WhiteboardDSAHardTo do8Write a debounce functiontimers · functions WhiteboardCodingMed.To do9Design a URL shortenerstorage · scaling · redirects WhiteboardSystem designMed.To do10Design a notification systemmessaging · reliability · scale WhiteboardSystem designHardTo do11The site returns errors after a deployincident-response · release · database WhiteboardTroubleshootingMed.To do12A server runs out of disk spacelinux · filesystem · operations WhiteboardTroubleshootingMed.To do13A time you took ownership when it was not your jobownership · initiative · star WhiteboardBehaviourEasyTo do14A time you disagreed with your teamdisagreement · communication · star WhiteboardBehaviourMed.To do15A time you cut scope to hit a dateprioritisation · scope · star WhiteboardBehaviourMed.To do16Search in a rotated sorted arrayarray · search WhiteboardDSAMed.To do17Check that a tree is a valid search treetree · validation WhiteboardDSAMed.To do18Fewest coins to make an amountarray · optimisation WhiteboardDSAMed.To do19Retry a function with exponential backoff and jitterasync · resilience · testing WhiteboardCodingMed.To do20A token-bucket rate limiter classstate · time · testing WhiteboardCodingMed.To do21Top N clients in an access logsorting · text-processing · counting WhiteboardCodingEasyTo do22A container restarts again and again after a releasekubernetes · incident-response · containers WhiteboardTroubleshootingEasyTo do23API latency doubled but errors stayed flatlatency · database · performance WhiteboardTroubleshootingMed.To do24Users cannot open the site: certificate or DNS?networking · incident-response · web WhiteboardTroubleshootingEasyTo do25Design a least-recently-used cachedesign · cache WhiteboardDSAMed.To do26Trapping rain waterarray · heights WhiteboardDSAHardTo do27Design a rate limiter for an APIrate-limiting · distributed-systems · api WhiteboardSystem designMed.To do