On the independence number of graphs with maximum degree 3

  • Authors:
  • Iyad A. Kanj;Fenghui Zhang

  • Affiliations:
  • School of Computing, DePaul University, Chicago, IL;Google Kirkland, Kirkland, WA

  • Venue:
  • WG'11 Proceedings of the 37th international conference on Graph-Theoretic Concepts in Computer Science
  • Year:
  • 2011

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Abstract

Let G be an undirected graph with maximum degree at most 3 such that G does not contain any of the three graphs shown in Figure [1] as a subgraph. We prove that the independence number of G is at least n(G)/3+nt(G)/42, where n(G) is the number of vertices in G and nt(G) is the number of nontriangle vertices in G. This bound is tight as implied by the well-known tight lower bound of 5n(G)/14 on the independence number of triangle-free graphs of maximum degree at most 3. We then proceed to show some algorithmic applications of the aforementioned combinatorial result to the area of parameterized complexity. We present a linear-time kernelization algorithm for the independent set problem on graphs with maximum degree at most 3 that computes a kernel of size at most 140 k/47