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The four-in-a-tree problem in triangle-free graphs

Author

Listed:
  • Nicolas Derhy

    (CEDRIC - Centre d'études et de recherche en informatique et communications - ENSIIE - Ecole Nationale Supérieure d'Informatique pour l'Industrie et l'Entreprise - CNAM - Conservatoire National des Arts et Métiers [CNAM] - HESAM - HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université)

  • Christophe Picouleau

    (CEDRIC - Centre d'études et de recherche en informatique et communications - ENSIIE - Ecole Nationale Supérieure d'Informatique pour l'Industrie et l'Entreprise - CNAM - Conservatoire National des Arts et Métiers [CNAM] - HESAM - HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université)

  • Nicolas Trotignon

    (CES - Centre d'économie de la Sorbonne - UP1 - Université Paris 1 Panthéon-Sorbonne - CNRS - Centre National de la Recherche Scientifique)

Abstract

The three-in-a-tree algorithm of Chudnovsky and Seymour decides in time O(n4) whether three given vertices of a graph belong to an induced tree. Here, we study four-in-a-tree for triangle-free graphs. We give a structural answer to the following question : how does look like a triangle-free graph such that no induced tree covers four given vertices ? Our main result says that any such graph must have the "same structure", in a sense to be defined precisely, as a square or a cube. We provide an O(nm)-time algorithm that given a triangle-free graph G together with four vertices outputs either an induced tree that contains them or a partition of V(G) certifying that no such tree exists. We prove that the problem of deciding whether there exists a tree T covering the four vertices such that at most one vertex of T has degree at least 3 is NP-complete.

Suggested Citation

  • Nicolas Derhy & Christophe Picouleau & Nicolas Trotignon, 2008. "The four-in-a-tree problem in triangle-free graphs," Université Paris1 Panthéon-Sorbonne (Post-Print and Working Papers) halshs-00270623, HAL.
    • Handle: RePEc:hal:cesptp:halshs-00270623
    Note: View the original document on HAL open archive server: https://shs.hal.science/halshs-00270623
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