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Dichotomy study of the Steiner tree problem in split-like graphs

cs.DM2026-05v1license

Abstract

Given a connected graph GG and a terminal set RV(G)R \subseteq V(G), the minimum Steiner tree problem (ST) asks for a tree that spans all of RR with at most rr vertices from V(G)\RV(G)\backslash R, for some integer r0r\geq 0. A \emph{split graph} is a graph which can be partitioned into a clique and an independent set. It is known from (Garey et al.,1977) that ST is NP-complete, even for split graphs . We introduce the class of split-like graphs which unifies several known graph classes like bipartite graphs, split graphs, and bisplit graphs, allowing for a cohesive study across multiple structural constraints. We investigate the computational complexity of the Steiner tree problem under structural constraints, specifically K1,rK_{1,r}-free, bounded diameter, chordality and star-convexity. Through reductions (primarily from Exact-3-Cover and its variants), the paper establishes a series of dichotomy results. It precisely gives the boundary for K1,rK_{1,r}-free bipartite graphs: ST is in P for r3r \le 3 and NP-complete for r4r \ge 4; whereas on K1,rK_{1,r}-free bisplit graphs, ST is in P for any fixed r3r\geq 3. On bisplit graphs, the Steiner tree problem admits a polynomial-time solution when the diameter is 2. In contrast, for diameters 3 and 4, the problem is NP-complete. The problem is NP-complete under star convexity constraints on the independent set. When star convexity is imposed on the kk-clique side, the problem is solvable in polynomial time. The problem is NP-complete on chordal bipartite graphs and chordal split graphs (i.e., split graphs themselves), while polynomial-time algorithms exist for other subclasses of split-like graphs.

Cite

@article{arxiv.2605.29540,
  title  = {Dichotomy study of the Steiner tree problem in split-like graphs},
  author = {Jyothish S and Sadagopan Narasimhan},
  journal= {arXiv preprint arXiv:2605.29540},
  year   = {2026}
}