{"title":"Reachability in graphs having linear 2-arboricity two is NL-hard","authors":"Ronak Bhadra, Raghunath Tewari","doi":"10.1016/j.ipl.2025.106611","DOIUrl":null,"url":null,"abstract":"<div><div>A linear <em>k</em>-diforest is a directed forest consisting of directed paths of length at most <em>k</em>. Linear <em>k</em>-arboricity of a directed graph is defined as the minimum number of linear <em>k</em>-diforests needed to partition the edges of the graph. We show that the problem of deciding reachability in directed graphs having linear 2-arboricity two is <span><math><mi>NL</mi></math></span>-hard and the same is also true for directed graphs having linear 1-arboricity three. Our proof also implies that deciding reachability in such graphs remains hard even when a decomposition into two linear 2-diforests or three linear 1-diforests is provided. We further extend our results for a more restricted notion of linear arboricity, called geometric linear arboricity.</div></div>","PeriodicalId":56290,"journal":{"name":"Information Processing Letters","volume":"192 ","pages":"Article 106611"},"PeriodicalIF":0.6000,"publicationDate":"2025-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Information Processing Letters","FirstCategoryId":"94","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0020019025000559","RegionNum":4,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"COMPUTER SCIENCE, INFORMATION SYSTEMS","Score":null,"Total":0}
引用次数: 0
Abstract
A linear k-diforest is a directed forest consisting of directed paths of length at most k. Linear k-arboricity of a directed graph is defined as the minimum number of linear k-diforests needed to partition the edges of the graph. We show that the problem of deciding reachability in directed graphs having linear 2-arboricity two is -hard and the same is also true for directed graphs having linear 1-arboricity three. Our proof also implies that deciding reachability in such graphs remains hard even when a decomposition into two linear 2-diforests or three linear 1-diforests is provided. We further extend our results for a more restricted notion of linear arboricity, called geometric linear arboricity.
期刊介绍:
Information Processing Letters invites submission of original research articles that focus on fundamental aspects of information processing and computing. This naturally includes work in the broadly understood field of theoretical computer science; although papers in all areas of scientific inquiry will be given consideration, provided that they describe research contributions credibly motivated by applications to computing and involve rigorous methodology. High quality experimental papers that address topics of sufficiently broad interest may also be considered.
Since its inception in 1971, Information Processing Letters has served as a forum for timely dissemination of short, concise and focused research contributions. Continuing with this tradition, and to expedite the reviewing process, manuscripts are generally limited in length to nine pages when they appear in print.