90. Design a Book Seller Aggregator Platform
Buy the cheapest offer under a maximum price from 1,000 sellers: cached offers, coalesced quotes, a hold-order-capture saga, open requests.
ClassicMedium
Designs
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Classic designs 38
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92. Design Online Chess
Real-time rated chess with server-validated moves, lag-compensated clocks, pairing by rating and a million watchers on one game.
ClassicMedium93. Design a Real-Time Game Leaderboard
Rank 200 million players in real time with sharded Redis sorted sets, count every game exactly once, and close a season fairly.
ClassicMedium95. Design a Team Chat App like Slack
Design a team chat app like Slack: channels and DMs in real time, threads, unread counts and search. One-hour boards for junior, senior and staff, with the theory behind them.
ClassicMedium96. Design a Food Delivery App like Uber Eats
Find restaurants that deliver to you, check out without double charges, time couriers to the kitchen and track them live.
ClassicMedium98. Design a Double-Entry Ledger
Record every money movement as balanced, append-only entries, exactly once, with holds, payouts and reconciliation.
ClassicMedium99. Design a Cross-Product Tagging System
One set of tags across Jira issues, Confluence pages and Bitbucket pull requests: batch renders, tag pages that never leak, suggestions, popular tags.
ClassicMedium101. Design a Webhook Delivery System
Signed HTTPS callbacks for a billion events a day, at least once, retried for three days, with no endpoint able to slow another.
ClassicMedium