文摘
In the Group Feedback Edge Set (\(\ell \)) (Group FES(\(\ell \))) problem, the input is a group-labeled graph G over a group \(\varGamma \) of order \(\ell \) and an integer k and the objective is to test whether there exists a set of at most k edges intersecting every non-null cycle in G. The study of the parameterized complexity of Group FES(\(\ell \)) was motivated by the fact that it generalizes the classical Edge Bipartization problem when \(\ell =2\). Guillemot [IWPEC 2008, Discrete Optimization 2011] initiated the study of the parameterized complexity of this problem and proved that it is fixed-parameter tractable (FPT) parameterized by k. Subsequently, Wahlström [SODA 2014] and Iwata et al. [2014] presented algorithms running in time \({\mathcal {O}}(4^kn^{{\mathcal {O}}(1)})\) (even in the oracle access model) and \({\mathcal {O}}(\ell ^{2k}m)\) respectively. In this paper, we give an algorithm for Group FES(\(\ell \)) running in time \({\mathcal {O}}(4^kk^{3}\ell (m+n))\). Our algorithm matches that of Iwata et al. when \(\ell =2\) (upto a multiplicative factor of \(k^3\)) and gives an improvement for \(\ell >2\).