Given an edge-weighted graph G on n nodes, the NP-hard Max-Cut problem asks for a node bipartition such that the sum of edge weights joining the different partitions is maximized. We propose a fixed-parameter tractable algorithm parameterized by the number k of crossings in a given drawing of G. Our algorithm achieves a running time of O(2 k · p(n + k)), where p is the polynomial running time for planar Max-Cut. The only previously known similar algorithm [8] is restricted to embedded 1-planar graphs (i.e., at most one crossing per edge) and its dependency on k is of order 3 k . Finally, combining this with the fact that crossing number is fixed-parameter tractable w.r.t. itself, we see that Max-Cut is fixed-parameter tractable w.r.t. the crossing number, even without a given drawing. Moreover, the results naturally carry over to the minor crossing number.
arXiv:1903.06061v2 [cs.DS] 6 Sep 2019QUBO such as multicommodity-flow problems, maximum clique, vertex cover, scheduling, and many others. Also see [10,11] for a more in-depth overview on applications.The Max-Cut problem has been shown to be NP-hard for general graphs [24]. Papadimitriou and Yannakakis [36] have shown that the Max-Cut problem is even APX-hard, i.e., there does not exist a polynomial-time approximation scheme unless P=NP. Goemans and Williamson proposed a randomized constant-factor approximation algorithm [17], which has been derandomized by Mahajan and Ramesh [31], achieving a ratio of 0.87856. Several special cases of the problem allow polynomial algorithms: If the weights of all edges are negative we obtain a Min-Cut problem, which can be solved, e.g., via network flow. Other special cases are, e.g., graphs without long odd cycles [20] or weakly bipartite graphs [19]. The case of planar input graphs is of particular interest. Orlova and Dorfman [34] and Hadlock [21] have shown how to solve Max-Cut in polynomial time for unweighted planar graphs. Those algorithms can be extended to weighted planar graphs; the currently fastest algorithms for the weighted case have been suggested by Shih et al. [38] and by Liers and Pardella [30], and achieve a running time of p(n) = O(n 3/2 log n) on planar graphs with n nodes. Barahona has shown that the planarity condition can be relaxed to graphs not contractible to K 5 [3] and to toroidal graphs (i.e., graphs that can be embedded on a genus-1 surface) with edge weights ±1 [2].Similarly, it has been shown that Max-Cut can be solved in polynomial time if the graph can be embedded on a surface of constant genus g [14,15]. However, the edge-weights have to be restricted to integers whose absolute values are bounded by a polynomial in the input. The central idea of this algorithm is to write the generating function of cuts as a linear combination of 4 g Pfaffians. This algorithm is in fact highly non-trivial to realize: In order to obtain an implementable algorithm, [15] reports on a scheme, which depends on the existence of sufficiently many prime numbers within a given interval, which cannot be guaranteed in ...