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Succinct indices for path minimum, with applications to path reporting. (English) Zbl 1365.68174
Schulz, Andreas S. (ed.) et al., Algorithms – ESA 2014. 22nd annual European symposium, Wrocław, Poland, September 8–10, 2014. Proceedings. Berlin: Springer (ISBN 978-3-662-44776-5/pbk). Lecture Notes in Computer Science 8737, 247-259 (2014).
Summary: In the path minimum query problem, we preprocess a tree on \(n\) weighted nodes, such that given an arbitrary path, we can locate the node with the smallest weight along this path. We design novel succinct indices for this problem; one of our index structures supports queries in \(O(\alpha (m,n))\) time, and occupies \(O(m)\) bits of space in addition to the space required for the input tree, where \(m\) is an integer greater than or equal to \(n\) and \(\alpha (m,n)\) is the inverse-Ackermann function. These indices give us the first succinct data structures for the path minimum problem, and allow us to obtain new data structures for path reporting queries, which report the nodes along a query path whose weights are within a query range. We achieve three different time/space tradeoffs for path reporting by designing (a) an \(O(n)\)-word structure with \(O(\lg^\varepsilon n + \mathrm{occ} \cdot \lg^\varepsilon n)\) query time, where \(\mathrm{occ}\) is the number of nodes reported; (b) an \(O(n\lg\lg n)\)-word structure with \(O(\lg\lg n + \mathrm{occ} \cdot \lg\lg n)\) query time; and (c) an \(O( n \lg^\varepsilon n)\)-word structure with \(O(\lg\lg n + \mathrm{occ})\) query time. These tradeoffs match the state of the art of two-dimensional orthogonal range reporting queries [T. M. Chan et al., in: Proceedings of the 27th annual symposium on computational geometry, SoCG 2011, Paris, France, 2011. New York, NY: Association for Computing Machinery (ACM). 1–10 (2011; Zbl 1283.68139)] which can be treated as a special case of path reporting queries. When the number of distinct weights is much smaller than \(n\), we further improve both the query time and the space cost of these three results.
For the entire collection see [Zbl 1295.68031].

MSC:
68P05 Data structures
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