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2010 IEEE 51st Annual Symposium on Foundations of Computer Science (2010)
Las Vegas, Nevada USA
Oct. 23, 2010 to Oct. 26, 2010
ISSN: 0272-5428
ISBN: 978-0-7695-4244-7
pp: 601-610
For an undirected $n$-vertex planar graph $G$ with non-negative edge-weights, we consider the following type of query: given two vertices $s$ and $t$ in $G$, what is the weight of a min $st$-cut in $G$? We show how to answer such queries in constant time with $O(n\log^5n)$ preprocessing time and $O(n\log n)$ space. We use a Gomory-Hu tree to represent all the pair wise min $st$-cuts implicitly. Previously, no sub quadratic time algorithm was known for this problem. Our oracle can be extended to report the min $st$-cuts in time proportional to their size. Since all-pairs min $st$-cut and the minimum cycle basis are dual problems in planar graphs, we also obtain an implicit representation of a minimum cycle basis in $O(n\log^5n)$ time and $O(n\log n)$ space and an explicit representation with additional $O(C)$ time and space where $C$ is the size of the basis. To obtain our results, we require that shortest paths be unique, this assumption can be removed deterministically with an additional $O(\log^2 n)$ running-time factor.
Graph theory, Algorithms, Networks

C. Wulff-Nilsen, P. Sankowski and G. Borradaile, "Min st-cut Oracle for Planar Graphs with Near-Linear Preprocessing Time," 2010 IEEE 51st Annual Symposium on Foundations of Computer Science(FOCS), Las Vegas, Nevada USA, 2010, pp. 601-610.
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