桶关键值图？

Question

I need a structure where I can push Key Values where the Keys are ordered ascending. If I request a Value to a Key, I would like to get the Value of the nearest bigger (but not equal) Key inside of the Map.

So for example, I do push 100, 500 and 1000. If I request 750 I do get the 1000 Value. If I request 450 I get the 500 Value. If I request 500, I get the 1000 value. Those keys are dynamic, a switch isn't possible here.

My approach would be to push a Class with a key and a value to a vector but this would last in a O(n).

Is there a better way/faster way to implement this instead of iterating forward through a Key vector and compare?

Answer 1

I think you should use std::map as the container. and use std::map::upper_bound to find the nearest bigger key.

In case of equal is acceptable, use std::map::lower_bound .

std::map::upper_bound and std::map::lower_bound is guaranteed the complexity as O(log(n)).

By the way, if you still want to use std::vector , std::upper_bound and std::lower_bound is guaranteed to have complexity as O(log(n)) for std::vector

Answer 2

Use std::map and std::map::upper_bound() . std::map is implemented as a tree, so std::map::upper_bound() is guaranteed to be O(log(n)).

std::map is sorted by the key using a given comparison function (default: std::less ). It include should everything you need.

Answer 3

you can use heap(min-heap or max-heap). insert delete or find is O(log(n)), and easy to implement. in fact it is similar to map, but you can code by you idea.