## Abstract

We give algorithms with running time 2O(klogk)·nO(1) for the following problems. Given an n-vertex unit disk graph G and an integer k, decide whether G containsa path on exactly/at least k vertices,a cycle on exactly k vertices,a cycle on at least k vertices,a feedback vertex set of size at most k, anda set of k pairwise vertex-disjoint cycles. For the first three problems, no subexponential time parameterized algorithms were previously known. For the remaining two problems, our algorithms significantly outperform the previously best known parameterized algorithms that run in time 2O(k0.75logk)·nO(1). Our algorithms are based on a new kind of tree decompositions of unit disk graphs where the separators can have size up to k^{O} ^{(} ^{1} ^{)} and there exists a solution that crosses every separator at most O(k) times. The running times of our algorithms are optimal up to the log k factor in the exponent, assuming the exponential time hypothesis.

Original language | English |
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Pages (from-to) | 879-911 |

Number of pages | 33 |

Journal | Discrete and Computational Geometry |

Volume | 62 |

Issue number | 4 |

DOIs | |

State | Published - 1 Dec 2019 |

## Keywords

- Cycle packing
- Feedback vertex set
- Longest cycle
- Longest path
- Parameterized complexity
- Unit disk graph
- Unit square graph

## ASJC Scopus subject areas

- Theoretical Computer Science
- Geometry and Topology
- Discrete Mathematics and Combinatorics
- Computational Theory and Mathematics