Hardness of Vertex Splitting: Cographs, Chordal Graphs, and Beyond

Satyabrata Jana; Shivesh K. Roy; R. B. Sandeep

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arXiv · 2607.13517

Hardness of Vertex Splitting: Cographs, Chordal Graphs, and Beyond

Satyabrata Jana·Shivesh K. Roy·R. B. Sandeep

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Abstract

Vertex splitting replaces a vertex (v) by two nonadjacent vertices whose neighborhoods together equal (N(v)). A split is \emph{exclusive} if these neighborhoods are disjoint and \emph{shallow} if no newly created vertex is split again. For a graph property (\Pi), \textsc{(\Pi)-Vertex Splitting} asks whether at most (k) splits can transform a graph (G) into one satisfying (\Pi). We continue the systematic study of this operation and settle several open problems. First, we prove that \textsc{Cograph Vertex Splitting} is \textsf{NP}-complete, even on graphs of girth at least 5, resolving a question of Firbas and Sorge (ISAAC 2024). More generally, \textsc{(P_t)-free Vertex Splitting} is \textsf{NP}-complete for every fixed (t\geq 4). We also prove that \textsc{Chordal Vertex Splitting} and \textsc{Unit-Interval Vertex Splitting} are \textsf{NP}-complete, resolving two questions of Abu-Khzam, Chakraborty, Isenmann, and Oijid (IWOCA 2026). Our hardness results extend to the exclusive and shallow variants. Assuming the Exponential Time Hypothesis, none of these problems admits an algorithm running in (2^{o(k)}n^{O(1)}) time; moreover, except for the unit-interval cases, none admits an algorithm running in (2^{o(n)}) time.

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Satyabrata Jana, Shivesh K. Roy, R. B. Sandeep. 2026-07-15. Hardness of Vertex Splitting: Cographs, Chordal Graphs, and Beyond. https://arxiv.org/abs/2607.13517

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