Mutable Priority Queue Container

When dealing with functional minimization, or maximization, it can sometimes be solved by a greedy algorithm. To implement greedy algorithm one needs priority queue container, i.e. get for a very low cost the lowest or highest element present in a sorted container. Whenever the priority of one element present in the queue needs to be modified, standard implementations, like \code{std::priority\_queue}, can not be applied directly. VTK has is own implementation \code{vtkPriorityQueue} which is not templated and can only be applied for \code{vtkIdType} and for the minimizing the functional. We propose here an implementation of a mutable priority queue container where element, priority, and objective (minimization or maximization) are given by template arguments. Our implementation allows to minimize or maximize a given functional, and any element can be modified, deleted at any time, and with a low cost.