Data-structure that stores unique elements but answers queries for another ordering in C++

is there a data structure, which stores its elements uniquely (for a given compare-Functor) but answers queries for the highest element in that data structure with respect to another compare-Function ?

For Example: I have a class with two properties :

1) the size

2) the value

I'd like to have a data structure which stores all elements uniquely regarding its size but answers queries for the element with the highest value.

Using std::set with a compare functor for the sizes gives me uniqueness but queries for the highest value will have linear runtime...

Is there a better way?

开发者_开发问答(I'll 'add elements then ask for the highest value' and keep iterating this until a certain termination point is reached)

Any information would be appreciated (papers etc)

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Boost::MultiIndex comes to mind.

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What you want can be achieved using the library Boost.Multi-index

Check in particular this example in the tutorial, which is very close to your use case.

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Could it be a kd-tree (k-dimensional tree)? In your case, k would be 2.