Dominating set based exact algorithms for 3-coloring

  • Authors:
  • N. S. Narayanaswamy;C. R. Subramanian

  • Affiliations:
  • Department of CSE, IIT Madras, Chennai, India;The Institute of Mathematical Sciences, Chennai, India

  • Venue:
  • Information Processing Letters
  • Year:
  • 2011

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Abstract

We show that the 3-colorability problem can be solved in O(1.296^n) time on any n-vertex graph with minimum degree at least 15. This algorithm is obtained by constructing a dominating set of the graph greedily, enumerating all possible 3-colorings of the dominating set, and then solving the resulting 2-list coloring instances in polynomial time. We also show that a 3-coloring can be obtained in 2^o^(^n^) time for graphs having minimum degree at least @w(n) where @w(n) is any function which goes to ~. We also show that if the lower bound on minimum degree is replaced by a constant (however large it may be), then neither a 2^o^(^n^) time nor a 2^o^(^m^) time algorithm is possible (m denotes the number of edges) for 3-colorability unless Exponential Time Hypothesis (ETH) fails. We also describe an algorithm which obtains a 4-coloring of a 3-colorable graph in O(1.2535^n) time.