Journal of Computer and System Sciences最新文献

{"title":"Triangle evacuation of 2 agents in the wireless model & the power of choosing a starting point","authors":"Konstantinos Georgiou ,&nbsp;Woojin Jang","doi":"10.1016/j.jcss.2025.103695","DOIUrl":"10.1016/j.jcss.2025.103695","url":null,"abstract":"<div><div>The input to the <em>Triangle Evacuation</em> problem is a non-obtuse triangle <em>ABC</em>. A feasible solution is two unit-speed trajectories of mobile agents that start at some point on the perimeter and eventually visit every point on the perimeter of <em>ABC</em>. The goal is to find trajectories that minimize the evacuation cost, defined as the supremum, over all points <em>T</em>, of the time when <em>T</em> is first visited by one agent plus the distance from <em>T</em> to the other agent at that time. We introduce 4 different algorithmic problems arising by letting the starting edge and/or the starting point <em>S</em> on that edge to be chosen either by the algorithm or the adversary. To that end, we provide a tight analysis for the algorithm that has been proved to be optimal for the previously studied search domains, as well as we provide lower bounds for each of the problems.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"155 ","pages":"Article 103695"},"PeriodicalIF":0.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144766445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Making the interval membership width of temporal graphs connected and bidirectional","authors":"Filippos Christodoulou ,&nbsp;Pierluigi Crescenzi ,&nbsp;Andrea Marino ,&nbsp;Ana Silva ,&nbsp;Dimitrios M. Thilikos","doi":"10.1016/j.jcss.2025.103684","DOIUrl":"10.1016/j.jcss.2025.103684","url":null,"abstract":"<div><div>Temporal graphs are graphs that evolve over time. Many problems which are polynomial-time solvable in standard graphs become <span>NP</span>-hard when appropriately defined in the realm of temporal graphs.This suggested the definition of several parameters for temporal graphs and to prove the fixed-parameter tractability of several problems with respect to these parameters. In this paper, we introduce a hierarchy of parameters based on the previously defined interval membership width and the temporal evolution of the connected components of the underlying static graph. We show that the Eulerian trail problem and the temporal 2-coloring problem are both fixed-parameter tractable with respect to any parameter in the hierarchy. We also introduce a vertex-variant of the parameters and show that the firefighter problem, known to be <span>FPT</span> with respect to the vertex-variant of the interval membership width, is also <span>FPT</span> with respect to one of the parameters in the second level of the hierarchy.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"155 ","pages":"Article 103684"},"PeriodicalIF":1.1,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144571103","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Approximate selection with unreliable comparisons in sublinear time","authors":"Shengyu Huang ,&nbsp;Chih-Hung Liu ,&nbsp;Daniel Rutschmann","doi":"10.1016/j.jcss.2025.103699","DOIUrl":"10.1016/j.jcss.2025.103699","url":null,"abstract":"<div><div>Given <em>n</em> elements, an integer <span><math><mi>k</mi><mo>≤</mo><mfrac><mrow><mi>n</mi></mrow><mrow><mn>2</mn></mrow></mfrac></math></span> and a parameter <span><math><mi>ε</mi><mo>≥</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mi>n</mi></mrow></mfrac></math></span>, we study the problem of selecting an element with rank in <span><math><mo>(</mo><mi>k</mi><mo>−</mo><mi>n</mi><mi>ε</mi><mo>,</mo><mi>k</mi><mo>+</mo><mi>n</mi><mi>ε</mi><mo>]</mo></math></span> using <em>unreliable</em> comparisons where the outcome of each comparison is incorrect independently with a constant error probability, and multiple comparisons between the same pair of elements are independent. We develop a randomized algorithm that performs <em>expected</em> <span><math><mi>O</mi><mo>(</mo><mfrac><mrow><mi>k</mi></mrow><mrow><mi>n</mi></mrow></mfrac><msup><mrow><mi>ε</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mi>log</mi><mo>⁡</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mi>Q</mi></mrow></mfrac><mo>)</mo></math></span> comparisons to achieve success probability at least <span><math><mn>1</mn><mo>−</mo><mi>Q</mi></math></span>. We also prove that even in the absence of comparison faults, any randomized algorithm with success probability at least <span><math><mn>1</mn><mo>−</mo><mi>Q</mi></math></span> performs <em>expected</em> <span><math><mi>Ω</mi><mo>(</mo><mi>min</mi><mo>⁡</mo><mo>{</mo><mi>n</mi><mo>,</mo><mfrac><mrow><mi>k</mi></mrow><mrow><mi>n</mi></mrow></mfrac><msup><mrow><mi>ε</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mi>log</mi><mo>⁡</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mi>Q</mi></mrow></mfrac><mo>}</mo><mo>)</mo></math></span> comparisons. In particular, our algorithm is optimal as long as <em>n</em> is large enough, i.e., when <span><math><mi>n</mi><mo>=</mo><mi>Ω</mi><mrow><mo>(</mo><mfrac><mrow><mi>k</mi></mrow><mrow><mi>n</mi></mrow></mfrac><msup><mrow><mi>ε</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mi>log</mi><mo>⁡</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mi>Q</mi></mrow></mfrac><mo>)</mo></mrow></math></span>; outside this parameter range, no algorithm performs a sublinear number of comparisons. Surprisingly, for constant <em>Q</em>, our algorithm performs expected <span><math><mi>O</mi><mo>(</mo><mfrac><mrow><mi>k</mi></mrow><mrow><mi>n</mi></mrow></mfrac><msup><mrow><mi>ε</mi></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mo>)</mo></math></span> comparisons with and without comparison faults, while for the exact selection problem, the expected number of comparisons is <span><math><mi>Θ</mi><mo>(</mo><mi>n</mi><mi>log</mi><mo>⁡</mo><mi>k</mi><mo>)</mo></math></span> with faults versus <span><math><mi>Θ</mi><mo>(</mo><mi>n</mi><mo>)</mo></math></span> without faults.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"155 ","pages":"Article 103699"},"PeriodicalIF":0.9,"publicationDate":"2026-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144886722","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"State complexity of one-way quantum finite automata together with classical states","authors":"Ligang Xiao ,&nbsp;Daowen Qiu","doi":"10.1016/j.jcss.2025.103659","DOIUrl":"10.1016/j.jcss.2025.103659","url":null,"abstract":"<div><div>One-way quantum finite automata together with classical states (1QFAC) proposed by Qiu et al. is a new one-way quantum finite automata (1QFA) model that integrates quantum finite automata (QFA) and deterministic finite automata (DFA). The relationshipsand balances between quantum states and classical states in 1QFAC are still not clear. In this paper, we obtain the following results: (1) We optimize the bound given by Qiu et al. that characterizes the relationships between quantum basis states and classical states as well as the equivalent minimal DFA. (2) We give an upper bound showing how many classical states are needed upon reducing the quantum basis states of 1QFAC. (3) We give a lower bound on the classical state number of 1QFAC for recognizing any given regular language, and show that the lower bound is exact if the given language is finite. (4) We show that 1QFAC are exponentially more succinct than DFA and probabilistic finite automata (PFA) for some regular languages. (5) We point out essential relationships between 1QFAC, MO-1QFA and multi-letter 1QFA, and induce a result regarding quantitative relationships between multi-letter 1QFA and DFA.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103659"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143916823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Acyclic, star and injective colouring: A complexity picture for H-free graphs","authors":"Jan Bok ,&nbsp;Nikola Jedličková ,&nbsp;Barnaby Martin ,&nbsp;Pascal Ochem ,&nbsp;Daniël Paulusma ,&nbsp;Siani Smith","doi":"10.1016/j.jcss.2025.103662","DOIUrl":"10.1016/j.jcss.2025.103662","url":null,"abstract":"<div><div>A (proper) colouring is acyclic, star, or injective if any two colour classes induce a forest, star forest or disjoint union of vertices and edges, respectively. The corresponding decision problems are <span>Acyclic Colouring</span>, <span>Star Colouring</span> and <span>Injective Colouring</span>. We give almost complete complexity classifications for <span>Acyclic Colouring</span>, <span>Star Colouring</span> and <span>Injective Colouring</span> on <em>H</em>-free graphs (for each of the problems, we have one open case). Moreover, we give full complexity classifications if the number of colours <em>k</em> is fixed, that is, not part of the input. From our study it follows that for fixed <em>k</em>, the three problems behave in the same way, but this is no longer true if <em>k</em> is part of the input. To obtain several of our results we prove stronger complexity results that in particular involve the girth of a graph and the class of line graphs of multigraphs.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103662"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143935545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the parameterized complexity of lineal topologies (depth-first spanning trees) with many or few leaves","authors":"Benjamin Bergougnoux ,&nbsp;Nello Blaser ,&nbsp;Michael Fellows ,&nbsp;Petr Golovach ,&nbsp;Frances Rosamond ,&nbsp;Emmanuel Sam","doi":"10.1016/j.jcss.2025.103680","DOIUrl":"10.1016/j.jcss.2025.103680","url":null,"abstract":"<div><div>This paper considers four problems with possible applications in network design: Given a graph <em>G</em> with <span><math><mo>|</mo><mi>G</mi><mo>|</mo><mo>=</mo><mi>n</mi></math></span> and an integer <span><math><mi>k</mi><mo>≥</mo><mn>0</mn></math></span>, does <em>G</em> have a DFS tree with (i) ≤<em>k</em> leaves, (ii) ≥<em>k</em> leaves, (iii) <span><math><mo>≤</mo><mi>n</mi><mo>−</mo><mi>k</mi></math></span> leaves, and (iv) <span><math><mo>≥</mo><mi>n</mi><mo>−</mo><mi>k</mi></math></span> leaves? We show that all four problems are NP-hard. When parameterized by <em>k</em>, we prove that while (i) is para-NP-hard and (ii) is W[1]-hard, both (iii) and (iv) admit polynomial kernels with <span><math><mi>O</mi><mo>(</mo><msup><mrow><mi>k</mi></mrow><mrow><mn>3</mn></mrow></msup><mo>)</mo></math></span> vertices, implying FPT algorithms running in <span><math><msup><mrow><mi>k</mi></mrow><mrow><mi>O</mi><mo>(</mo><mi>k</mi><mo>)</mo></mrow></msup><mo>⋅</mo><msup><mrow><mi>n</mi></mrow><mrow><mi>O</mi><mo>(</mo><mn>1</mn><mo>)</mo></mrow></msup></math></span> time. Our polynomial kernels are based on a <span><math><mi>O</mi><mo>(</mo><mi>k</mi><mo>)</mo></math></span>-sized vertex cover structure associated with the solution of these problems. As a byproduct, we obtain polynomial kernels for these problems parameterized by the vertex cover number of the input graph.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103680"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144205444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The edit distance to k-subsequence universality","authors":"Joel D. Day ,&nbsp;Pamela Fleischmann ,&nbsp;Maria Kosche ,&nbsp;Tore Koß ,&nbsp;Florin Manea ,&nbsp;Stefan Siemer","doi":"10.1016/j.jcss.2025.103681","DOIUrl":"10.1016/j.jcss.2025.103681","url":null,"abstract":"<div><div>A word <em>u</em> is a subsequence of another word <em>w</em> if <em>u</em> is obtained from <em>w</em> by deleting some of its letters. In the 1970s, Simon defined the relation <span><math><msub><mrow><mo>∼</mo></mrow><mrow><mi>k</mi></mrow></msub></math></span> (called now Simon-Congruence) as follows: two words having the same set of subsequences of length <em>k</em> are <span><math><msub><mrow><mo>∼</mo></mrow><mrow><mi>k</mi></mrow></msub></math></span>-congruent. It is thus natural to ask, for non <em>k</em>-equivalent words <em>w</em> and <em>u</em>, what is the minimal number of edit operations that we need to perform on <em>w</em> to obtain a word which is <span><math><msub><mrow><mo>∼</mo></mrow><mrow><mi>k</mi></mrow></msub></math></span>-equivalent to <em>u</em>. Here, we consider this problem in a specific setting: when <em>u</em> is a <em>k</em>-subsequence universal word. A word <em>u</em> with <span><math><mi>a</mi><mi>l</mi><mi>p</mi><mi>h</mi><mo>(</mo><mi>u</mi><mo>)</mo><mo>=</mo><mi>Σ</mi></math></span> is called <em>k</em>-subsequence universal if the set of length-<em>k</em> subsequences of <em>u</em> contains all possible words of length <em>k</em> over Σ. As such, our results are a series of efficient algorithms computing the edit distance from <em>w</em> to the language of <em>k</em>-subsequence universal words.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103681"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144314092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Compact distributed certification of geometric graph classes","authors":"Benjamin Jauregui ,&nbsp;Pedro Montealegre ,&nbsp;Diego Ramirez-Romero ,&nbsp;Ivan Rapaport","doi":"10.1016/j.jcss.2025.103661","DOIUrl":"10.1016/j.jcss.2025.103661","url":null,"abstract":"<div><div>Distributed proofs allow network nodes to collectively verify if the network satisfies a given predicate. The most versatile mechanism, known as a proof labeling scheme (PLS), functions as the distributed equivalent of NP, where a non-trustable prover assigns each node a certificate. Nodes exchange these certificates with their neighbors to prove the graph satisfies the predicate, with the certificate size being the primary complexity measure. Many graph properties, like planarity or bounded tree-width, can be certified with <span><math><mi>O</mi><mo>(</mo><mi>log</mi><mo>⁡</mo><mi>n</mi><mo>)</mo></math></span>-bit certificates on <em>n</em>-node graphs.</div><div>This paper presents <span><math><mi>O</mi><mo>(</mo><mi>log</mi><mo>⁡</mo><mi>n</mi><mo>)</mo></math></span> distributed certifications for recognizing geometric graph classes commonly found in distributed systems: interval graphs, chordal graphs, circular arc graphs, trapezoid graphs, and permutation graphs. It also establishes tight lower bounds on the certificate sizes required for these geometric intersection graph classes, proving that the proposed certifications are optimal.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103661"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143935544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Weighted group search on the disk & improved lower bounds for priority evacuation","authors":"Konstantinos Georgiou,&nbsp;Xin Wang","doi":"10.1016/j.jcss.2025.103678","DOIUrl":"10.1016/j.jcss.2025.103678","url":null,"abstract":"<div><div>We study <em>weighted group search on a disk</em>, where two unit-speed agents must locate a hidden target exactly distance 1 away (within a unit-radius disk), starting from the same point. Agents share findings instantly via the <em>wireless</em> model. The goal is to minimize the worst-case <em>weighted average</em> of their arrival times, with one agent weighted 1 and the other <span><math><mi>w</mi><mo>∈</mo><mo>[</mo><mn>0</mn><mo>,</mo><mn>1</mn><mo>]</mo></math></span>. This problem extends prior work on search on a line (with known optimal strategies) and the <em>priority evacuation</em> problem, which corresponds to <span><math><mi>w</mi><mo>=</mo><mn>0</mn></math></span> and still has a notable gap between upper and lower bounds. Our contributions are the following: (1) Upper bounds for all <em>w</em>, using refined known techniques. (2) A novel lower-bound framework using linear programming, inspired by metric embeddings, and (3) Improved bounds for priority evacuation, raising the lower bound from 4.38962 to 4.56798.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103678"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144067992","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complexity framework for forbidden subgraphs IV: The Steiner Forest problem","authors":"Hans L. Bodlaender ,&nbsp;Matthew Johnson ,&nbsp;Barnaby Martin ,&nbsp;Jelle J. Oostveen ,&nbsp;Sukanya Pandey ,&nbsp;Daniël Paulusma ,&nbsp;Siani Smith ,&nbsp;Erik Jan van Leeuwen","doi":"10.1016/j.jcss.2025.103682","DOIUrl":"10.1016/j.jcss.2025.103682","url":null,"abstract":"<div><div>We study <span>Steiner Forest</span> on <em>H</em>-subgraph-free graphs, that is, graphs that do not contain some fixed graph <em>H</em> as a (not necessarily induced) subgraph. In contrast to the related <span>Steiner Tree</span> problem, <span>Steiner Forest</span> falls outside a recent framework that completely characterizes the complexity of many problems on <em>H</em>-subgraph-free graphs. Hence, the complexity of <span>Steiner Forest</span> on <em>H</em>-subgraph-free graphs remained open. Our main results are four polynomial-time algorithms for different excluded graphs <em>H</em> that are central to further understand its complexity. We also study the complexity of <span>Steiner Forest</span> for graphs with a small <em>c</em>-deletion set, that is, a small set <em>X</em> of vertices such that each connected component of <span><math><mi>G</mi><mo>−</mo><mi>X</mi></math></span> has size at most <em>c</em>. For this parameter, we give two algorithms that we later employ as subroutines (including a faster algorithm when <span><math><mi>c</mi><mo>=</mo><mn>1</mn></math></span>, that is, the vertex cover number) and exhibit a dichotomy theorem.</div></div>","PeriodicalId":50224,"journal":{"name":"Journal of Computer and System Sciences","volume":"154 ","pages":"Article 103682"},"PeriodicalIF":1.1,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144557500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}