Leaderboard with SortedSet

A leaderboard needs: insert a score, get the top N, get someone's rank, and do all of that without re-sorting the whole thing on every update.

Modeling entries

SortedSet compares whole objects, so model each entry as { player, score } and compare by score, breaking ties by name to keep results deterministic:

import { SortedSet } from 'sorted-collections';

interface Entry {
  player: string;
  score: number;
}

const leaderboard = new SortedSet<Entry>([], {
  comparator: (a, b) => a.score - b.score || a.player.localeCompare(b.player),
});

leaderboard.add({ player: 'ada', score: 1200 });
leaderboard.add({ player: 'grace', score: 980 });
leaderboard.add({ player: 'alan', score: 1500 });

Top N

Sorted ascending, so the top N is the last N elements. islice takes negative indices like Array.prototype.slice:

const topThree = [...leaderboard.islice(-3)].reverse();
// [{ player: 'alan', score: 1500 }, { player: 'ada', score: 1200 }, { player: 'grace', score: 980 }]

Someone's rank

indexOf needs an object equal under the comparator's rules — it doesn't have to be the same reference, just the same score/player:

const rank = leaderboard.length - leaderboard.indexOf({ player: 'ada', score: 1200 });
// rank === 2 (alan at 1500 is rank 1, ada at 1200 is rank 2)

Everyone in a score band

For a compound comparator like this one, build range bounds carefully: the tie-break field on a boundary object affects whether ties at the boundary get included. Use a value that sorts before everything for the low bound, and after everything for the high bound:

leaderboard.add({ player: 'bob', score: 1000 });
leaderboard.add({ player: 'amy', score: 1400 });
leaderboard.add({ player: 'zoe', score: 1400 });

// Everyone scoring between 1000 and 1400, inclusive — '' sorts before any real name,
// '￿' sorts after any real name, so ties exactly at 1000 or 1400 aren't dropped:
const band = [...leaderboard.irange({ player: '', score: 1000 }, { player: '￿', score: 1400 })];
// [bob(1000), ada(1200), amy(1400), zoe(1400)]

If your comparator only sorts by score (no tie-break), you can skip this and pass plain { score }-shaped bounds directly.

Updating a score

SortedSet doesn't have an in-place "update" — remove the old entry, add the new one:

leaderboard.discard({ player: 'grace', score: 980 });
leaderboard.add({ player: 'grace', score: 1050 });

See the API reference for the rest of SortedSet's methods, including union/intersection/difference for merging leaderboards across shards.