We consider succinct data structures for representing a set of n horizontal line segments in the plane given in rank space to support segment access, segment selection, and segment rank queries. A segment access query finds the segment (x₁, x₂, y) given its y-coordinate (y-coordinates of the segments are distinct), a segment selection query finds the jth smallest segment (the segment with the jth smallest y-coordinate) among the segments crossing the vertical line for a given x-coordinate, and a segment rank query finds the number of segments crossing the vertical line through x-coordinate i with y-coordinate at most y, for a given x and y. This problem is a central component in compressed data structures for persistent strings supporting random access. Our main result is a data structure using 2n lg n + O(n lg n / lg lg n) bits of space and O(lg n / lg lg n) query time for all operations. We show that this space bound is optimal up to lower-order terms. We will also show that the query time for segment rank is optimal. The query time for segment selection is also optimal by a previous bound. To obtain our results, we present a novel segment wavelet tree data structure of independent interest. This structure is inspired by and extends the classic wavelet tree for sequences. This leads to a simple, succinct solution with O(log n) query times. We then extend this solution to obtain optimal query time. Our space lower bound follows from a simple counting argument, and our lower bound for segment rank is obtained by a reduction from 2-dimensional counting.
@InProceedings{bille_et_al:LIPIcs.CPM.2025.27, author = {Bille, Philip and G{\o}rtz, Inge Li and Tarnow, Simon R.}, title = {{Succinct Data Structures for Segments}}, booktitle = {36th Annual Symposium on Combinatorial Pattern Matching (CPM 2025)}, pages = {27:1--27:14}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-369-0}, ISSN = {1868-8969}, year = {2025}, volume = {331}, editor = {Bonizzoni, Paola and M\"{a}kinen, Veli}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CPM.2025.27}, URN = {urn:nbn:de:0030-drops-231218}, doi = {10.4230/LIPIcs.CPM.2025.27}, annote = {Keywords: Succinct, Data structures, Selection} }
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