Let G = (V, E) be a 2-vertex-connected directed graph with m edges and n vertices. We consider the problem of approximating the smallest 2-vertex connected spanning subgraph (2VCSS) of G, and provide new efficient algorithms for this problem based on a clever use of low-high orders. The best previously known algorithms were able to compute a 3/2-approximation in O(m n+n 2) time, or a 3-approximation faster in linear time. In this paper, we present a linear-time algorithm that achieves a better approximation ratio of 2, and another algorithm that matches the previous 3/2-approximation in O(m n + n 2 ) time. We conducted a thorough experimental evaluation of all the above algorithms on a variety of input graphs. The experimental results show that both our two new algorithms perform well in practice. In particular, in our experiments the new 3/2-approximation algorithm was always faster than the previous 3/2-approximation algorithm, while their two approximation ratios were close. On the other side, our new linear-time algorithm yielded consistently better approximation ratios than the previously known linear-time algorithm, at the price of a small overhead in the running time.
@InProceedings{georgiadis_et_al:LIPIcs.SEA.2017.9,
author = {Georgiadis, Loukas and Italiano, Giuseppe F. and Karanasiou, Aikaterini},
title = {{Approximating the Smallest 2-Vertex-Connected Spanning Subgraph via Low-High Orders}},
booktitle = {16th International Symposium on Experimental Algorithms (SEA 2017)},
pages = {9:1--9:16},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-036-1},
ISSN = {1868-8969},
year = {2017},
volume = {75},
editor = {Iliopoulos, Costas S. and Pissis, Solon P. and Puglisi, Simon J. and Raman, Rajeev},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2017.9},
URN = {urn:nbn:de:0030-drops-76299},
doi = {10.4230/LIPIcs.SEA.2017.9},
annote = {Keywords: 2-vertex connectivity, approximation algorithms, directed graphs}
}