,
Hiroshi Eto
,
Mingyang Gong,
Jesper Jansson
,
Guohui Lin
,
Eiji Miyano
,
Hirotaka Ono
,
Shunichi Tanaka
Creative Commons Attribution 4.0 International license
We study the approximability of the Longest Run Subsequence problem (LRS for short). For a string S = s_1 ⋯ s_n over an alphabet Σ, a run of a symbol σ ∈ Σ in S is a maximal substring of consecutive occurrences of σ. A run subsequence S' of S is a sequence in which every symbol σ ∈ Σ occurs in at most one run. Given a string S, the goal of LRS is to find a longest run subsequence S^* of S such that the length |S^*| is maximized over all the run subsequences of S. It is known that LRS is APX-hard even if each symbol has at most two occurrences in the input string, and that LRS admits a polynomial-time k-approximation algorithm if the number of occurrences of every symbol in the input string is bounded by k. In this paper, we design a polynomial-time (k+1)/2-approximation algorithm for LRS under the k-occurrence constraint on input strings. For the case k = 2, we further improve the approximation ratio from 3/2 to 4/3.
@InProceedings{asahiro_et_al:LIPIcs.CPM.2023.2,
author = {Asahiro, Yuichi and Eto, Hiroshi and Gong, Mingyang and Jansson, Jesper and Lin, Guohui and Miyano, Eiji and Ono, Hirotaka and Tanaka, Shunichi},
title = {{Approximation Algorithms for the Longest Run Subsequence Problem}},
booktitle = {34th Annual Symposium on Combinatorial Pattern Matching (CPM 2023)},
pages = {2:1--2:12},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-276-1},
ISSN = {1868-8969},
year = {2023},
volume = {259},
editor = {Bulteau, Laurent and Lipt\'{a}k, Zsuzsanna},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CPM.2023.2},
URN = {urn:nbn:de:0030-drops-179560},
doi = {10.4230/LIPIcs.CPM.2023.2},
annote = {Keywords: Longest run subsequence problem, bounded occurrence, approximation algorithm}
}