Approximating longest directed paths and cycles
Author
Summary, in English
We investigate the hardness of approximating the longest path and the longest cycle in directed graphs on n vertices. We show that neither of these two problems can be polynomial time approximated within n(1-epsilon)for any epsilon > 0 unless P = NP. In particular, the result holds for digraphs of constant bounded outdegree that contain a Hamiltonian cycle. Assuming the stronger complexity conjecture that Satisfiability cannot be solved in subexponential time, we show that there is no polynomial time algorithm that finds a directed path of length Omega(f(n) log(2) n), or a directed cycle of length Omega(f(n) log n), for any nondecreasing, polynomial time computable function f in w(1). With a recent algorithm for undirected graphs by Gabow, this shows that long paths and cycles are harder to find in directed graphs than in undirected graphs. We also find a directed path of length Omega(log(2) n/log log n) in Hamiltonian digraphs with bounded outdegree. With our hardness results, this shows that long directed cycles are harder to find than a long directed paths. Furthermore, we present a simple polynomial time algorithm that finds paths of length Omega(n) in directed expanders of constant bounded outdegree.
Department/s
- Department of Computer Science
- Computer Science
- Parallel Systems
Publishing year
2004
Language
English
Pages
222-233
Publication/Series
Lecture Notes in Computer Science
Volume
3142
Document type
Journal article
Publisher
Springer
Topic
- Computer Science
Status
Published
ISBN/ISSN/Other
- ISSN: 1611-3349