Finding Detours is Fixed-parameter Tractable
Abstract
We consider the following natural "above guarantee" parameterization of the classical Longest Path problem: For given vertices s and t of a graph G, and an integer k, the problem Longest Detour asks for an (s,t)-path in G that is at least k longer than a shortest (s,t)-path. Using insights into structural graph theory, we prove that Longest Detour is fixed-parameter tractable (FPT) on undirected graphs and actually even admits a single-exponential algorithm, that is, one of running time exp(O(k)) poly(n). This matches (up to the base of the exponential) the best algorithms for finding a path of length at least k. Furthermore, we study the related problem Exact Detour that asks whether a graph G contains an (s,t)-path that is exactly k longer than a shortest (s,t)-path. For this problem, we obtain a randomized algorithm with running time about 2.746^k, and a deterministic algorithm with running time about 6.745^k, showing that this problem is FPT as well. Our algorithms for Exact Detour apply to both undirected and directed graphs.
Cite
@article{arxiv.1607.07737,
title = {Finding Detours is Fixed-parameter Tractable},
author = {Ivona Bezáková and Radu Curticapean and Holger Dell and Fedor V. Fomin},
journal= {arXiv preprint arXiv:1607.07737},
year = {2018}
}
Comments
Extended abstract appears at ICALP 2017