Abstract
We study the exact complexity of the Hamiltonian Cycle and the q-Colouring problem in disk graphs. We show that the Hamiltonian Cycle problem can be solved in \(2^{O(\sqrt{n})}\) on n-vertex disk graphs where the ratio of the largest and smallest disk radius is O(1). We also show that this is optimal: assuming the Exponential Time Hypothesis, there is no \(2^{o(\sqrt{n})}\)-time algorithm for Hamiltonian Cycle, even on unit disk graphs. We give analogous results for graph colouring: under the Exponential Time Hypothesis, for any fixed q, q-Colouring does not admit a \(2^{o(\sqrt{n})}\)-time algorithm, even when restricted to unit disk graphs, and it is solvable in \(2^{O(\sqrt{n})}\)-time on disk graphs.
The research of the first author was supported by the Netherlands Organisation for Scientific Research (NWO) under project no. 024.002.003.
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Acknowledgements
This work was initiated at the Lorentz Center workshop ‘Fixed-Parameter Computational Geometry’. We are grateful to Hans L. Bodlaender and Mark de Berg for discussions and their help with improving this paper.
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Kisfaludi-Bak, S., van der Zanden, T.C. (2017). On the Exact Complexity of Hamiltonian Cycle and q-Colouring in Disk Graphs. In: Fotakis, D., Pagourtzis, A., Paschos, V. (eds) Algorithms and Complexity. CIAC 2017. Lecture Notes in Computer Science(), vol 10236. Springer, Cham. https://doi.org/10.1007/978-3-319-57586-5_31
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