Abstract
It is an open problem whether the 3-coloring problem can be solved in polynomial time in the class of graphs that do not contain an induced path on t vertices, for fixed t. We propose an algorithm that, given a 3-colorable graph without an induced path on t vertices, computes a coloring with \(\max \left\{ 5,2\left\lceil \frac{t-1}{2}\right\rceil -2\right\} \) many colors. If the input graph is triangle-free, we only need \(\max \left\{ 4,\left\lceil \frac{t-1}{2}\right\rceil +1\right\} \) many colors. The running time of our algorithm is \(O((3^{t-2}+t^2)m+n)\) if the input graph has n vertices and m edges.
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Acknowledgements
We are thankful to Paul Seymour for many helpful discussions. We thank Stefan Hougardy for pointing out [20] to us. This material is based upon work supported in part by the U.S. Army Research Laboratory and the U.S. Army Research Office under Grant No. W911NF-16-1-0404.
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An extended abstract of the paper has previously appeared in Bodlaender H., Woeginger G. (eds): Graph-Theoretic Concepts in Computer Science (WG) 2017. Lecture Notes in Computer Science, vol 10520. Springer, Cham.
The first author was supported by National Science Foundation grant DMS-1550991 and US Army Research Office Grant W911NF-16-1-0404. The fourth author was supported by Fondecyt Grants 1140766 and 1180830, by CMM-Basal AFB 170001, and by Millennium Nucleus Information and Coordination in Networks.
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Chudnovsky, M., Schaudt, O., Spirkl, S. et al. Approximately Coloring Graphs Without Long Induced Paths. Algorithmica 81, 3186–3199 (2019). https://doi.org/10.1007/s00453-019-00577-6
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DOI: https://doi.org/10.1007/s00453-019-00577-6