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Asked: 2026-05-13T14:39:05+00:00

Here’s a description: It operates like a regular map with get , put ,

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Here’s a description:

It operates like a regular map with get, put, and remove methods, but has a getTopKEntries(int k) method to get the top-K elements, sorted by the key:

For my specific use case, I’m adding, removing, and adjusting a lot of values in the structure, but at any one time there’s approximately 500-1000 elements; I want to return the entries for the top 10 keys efficiently.

  • I call the put and remove methods many times.
  • I call the getTopKEntries method.
  • I call the put and remove methods some more times.
  • I call the getTopKEntries method.
  • …

I’m hoping for O(1) get, put, and remove operations, and for getTopKEntries to be dependent only on K, not on the size of the map.

So what’s a data structure for efficiently returning the top-K elements of a map?

My other question is similar, but is for the case of returning all elements of a map, sorted by the key.

If it helps, both the keys and values are 4-byte integers.

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1 Answer

  1. Editorial Team

    A binary search tree (i.e. std::map in C++) sounds like the perfect structure: it’s already lexicographically ordered, i.e. a simple in-order traversal will yield the elements in ascending order. Hence, iterating over the first k elements will yield the top k elements directly.

    Additionally, since you foresee a lot of “remove” operations, a hash table won’t be well-suited anyway: remove operations destroy the load factor characteristics of hash tables which leads to a rapid deterioration of the runtime.

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