On the Complexity of the Decisive Problem in Simple, Regular and Weighted Games

We study the computational complexity of an important property of simple, regular and weighted games, which is decisiveness. We show that this concept can naturally be represented in the context of hypergraph theory, and that decisiveness can be decided for simple games in quasipolynomial time, and for regular and weighted games in polynomial time. The strongness condition poses the main difficulties, while properness reduces the complexity of the problem, especially if it is amplified by regularity. On the other hand, regularity also allows to specify the problem instances much more economically, implying a reconsideration of the corresponding complexity measure that, as we prove, has important structural as well as algorithmic consequences.