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Designs with worked examples 3

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47. Design an Online Judge like LeetCode
Run strangers' code safely in single-use microVMs, return verdicts within 5 seconds, and rank 100,000 contestants live.
ClassicMedium
Caching Queues Databases
+8
Security AWS Firecracker Leaderboards Online judge Redis Sandboxing Amazon SQS
Worked design
Practice
59. Design a Fitness Tracking App like Strava
Record runs and rides on the phone without signal, upload each once, show them to friends and rank athletes by week, month and year.
ClassicMedium
Caching Databases AWS
+6
DynamoDB Fitness GPS Leaderboards Offline first Redis
Worked design
Practice
93. 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.
ClassicMedium
Caching Databases Streaming
+8
Distributed systems AWS Flink Gaming Kafka Leaderboards Redis Sorted sets
Worked design
Practice

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