Art of Codeartofcode
Lesson 14 of 15

35. Design a Leaderboard (Top-K)

1
The interview prompt
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35.1 What do you ask first?
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35.2 How big is this, really?
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35.3 What are the doors?
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35.4 What do we store?
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35.5 What does the whole system look like?
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35.6 How do sorted sets work for this?
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35.7 How do you handle real-time updates?
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35.8 How do you handle ties?
10
35.9 How do you shard a leaderboard?
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35.10 What would you say in the last five minutes?
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Score yourself
13
Variations to practise
14
Sources
15
Code lab
35. Design a Leaderboard (Top-K)

Sources

3 min read+10 XP

Source notes

  • Redis sorted set commands and their time complexities (ZADD O(log N), ZREVRANK O(log N), ZREVRANGE O(log N + M), ZCOUNT O(log N)): Redis command documentation.
  • Double-precision floats represent integers exactly up to 2⁵³: IEEE 754.
  • Contest sizes, pick rates, shard throughput and refresh rates are interview assumptions agreed in Step 1, not figures for any real app. Arithmetic computed 2026-10-08.
  • Sorted-set behaviour, fan-out share, composite tie scores, competition ranking, sharded top-K and rank, and histogram percentiles: tested 2026-10-08 (code/ch35_leaderboard.py, all checks pass).