Art of Codeartofcode
Lesson 9 of 15

35. Design a Leaderboard (Top-K)

1
The interview prompt
2
35.1 What do you ask first?
3
35.2 How big is this, really?
4
35.3 What are the doors?
5
35.4 What do we store?
6
35.5 What does the whole system look like?
7
35.6 How do sorted sets work for this?
8
35.7 How do you handle real-time updates?
9
35.8 How do you handle ties?
10
35.9 How do you shard a leaderboard?
11
35.10 What would you say in the last five minutes?
12
Score yourself
13
Variations to practise
14
Sources
15
Code lab
35. Design a Leaderboard (Top-K)

35.8 How do you handle ties?

3 min read+10 XP

With 20 million teams built from 22 players, many teams have exactly the same points, especially early in the match. Two decisions:

1. Ordering: who's listed first? Redis orders equal scores by member name, which is arbitrary. Define a rule, for example earlier joining wins, and encode it into the score:

score = points × 2 × 10¹⁰ + (10¹⁰ − joined_at)

(Points are scaled by 2 to keep half-points from the 1.5× vice-captain as integers.) More points always wins; for equal points, the earlier join has a higher score. In the chapter's code, 121.0 points beats 120.5, and for two teams on 120.5, the one that joined at time 500 beats the one at 900. Keep the composite well below 2⁵³ so it's exact as a double-precision score: check the ranges for your real numbers.

2. Display rank: do equal points share a rank? Most leaderboards show competition ranking ("1, 2, 2, 4"): tied teams share a rank, and the next rank skips. In the chapter's code, scores 90, 85, 85, 70 rank 1, 2, 2, 4. Prizes for tied ranks are usually split according to the contest rules, decided by the final job, not the live board.

Memory code: "Break ties with a rule you can explain, and show shared ranks honestly."