Uniquely Colourable Graphs and the Hardness of Colouring Graphs of Large Girth

  • Authors:
  • Thomas Emden-Weinert;Stefan Hougardy;Bernd Kreuter

  • Affiliations:
  • Institut für Informatik, Humboldt-Universität zu Berlin, 10099 Berlin, Germany (e-mail: TEmdenWe@vss.com hougardy@informatik.hu-berlin.de bernd.kreuter@sap-ag.de);Institut für Informatik, Humboldt-Universität zu Berlin, 10099 Berlin, Germany (e-mail: TEmdenWe@vss.com hougardy@informatik.hu-berlin.de bernd.kreuter@sap-ag.de);Institut für Informatik, Humboldt-Universität zu Berlin, 10099 Berlin, Germany (e-mail: TEmdenWe@vss.com hougardy@informatik.hu-berlin.de bernd.kreuter@sap-ag.de)

  • Venue:
  • Combinatorics, Probability and Computing
  • Year:
  • 1998

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Abstract

For any integer k, we prove the existence of a uniquely k-colourable graph of girth at least g on at most k12(g+1) vertices whose maximal degree is at most 5k13. From this we deduce that, unless NP=RP, no polynomial time algorithm for k-Colourability on graphs G of girth g(G)≥log∣G∣/13logk and maximum degree Δ(G)≤6k13 can exist. We also study several related problems.