I have a knapsack problem that has been frustrating me for weeks, in which we consider a set of n items, described by their integer value, and being of one of C colors.
There exists a constraint on the number of different colors of objects in the knapsack (but no "weight" constraint), and the goal is to maximize the value of the knapsack.
It's basically the same setting as in this model http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.22.9533&rep=rep1&type=pdf except that there is only one knapsack and the items are "weightless".
Is this problem hard, easy, yet to be classified? I would really appreciate any pointers. Please and thank you in advance.