22 Search Results for "Yamashita, Masafumi"

Document
DOI: 10.4230/LIPIcs.SoCG.2026.45
Line Segment Visibility in Simple Polygons: Exact, Robust, Scalable Computation and Applications

Authors: Sándor P. Fekete, Prahlad Narasimhan Kasthurirangan, Phillip Keldenich, Fabian Kollhoff, Chek-Manh Loi, and Michael Perk

Published in: LIPIcs, Volume 367, 42nd International Symposium on Computational Geometry (SoCG 2026)

Abstract
The weak visibility polygon of a line segment s inside a simple polygon P, denoted by V_P(s), is the region of the polygon that is visible from at least one point on s. Given its fundamental nature in computational geometry, several algorithms have been proposed to compute weak visibility polygons efficiently, each with different trade-offs in terms of preprocessing time, query time, and space complexity. Although there are many applications that require computing these polygons such as computer graphics, robot motion planning, and network communication systems, there is a lack of any implementations of these algorithms in the literature - not to mention one that is exact, robust, and scalable. Furthermore, weak segment visibility polygons are used as basic building blocks in several other algorithms, such as in minimum-link path computation. In this work, we present an implementation of an optimal linear-time algorithm for computing the weak visibility polygon of a segment inside a triangulated simple polygon. Our implementation provides exact, robust geometric primitives and optimizations to handle large inputs with more than 18,000,000 vertices. We demonstrate two concrete applications: (1) construction of window partitions, a standard data structure in visibility algorithms, and (2) support for optimal minimum-link path queries between two points in a simple polygon, the latter serving as a direct use case of the former. Experimental results on a variety of polygon families confirm that the end-to-end running time scales linearly with the size of the polygon and is dominated by the cost of computing the triangulation, validating the practicality and scalability of the approach. The implementation is released as open source in the format of a CGAL package to support reproducibility and further research.
Cite as

Sándor P. Fekete, Prahlad Narasimhan Kasthurirangan, Phillip Keldenich, Fabian Kollhoff, Chek-Manh Loi, and Michael Perk. Line Segment Visibility in Simple Polygons: Exact, Robust, Scalable Computation and Applications. In 42nd International Symposium on Computational Geometry (SoCG 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 367, pp. 45:1-45:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{fekete_et_al:LIPIcs.SoCG.2026.45,
  author =	{Fekete, S\'{a}ndor P. and Kasthurirangan, Prahlad Narasimhan and Keldenich, Phillip and Kollhoff, Fabian and Loi, Chek-Manh and Perk, Michael},
  title =	{{Line Segment Visibility in Simple Polygons: Exact, Robust, Scalable Computation and Applications}},
  booktitle =	{42nd International Symposium on Computational Geometry (SoCG 2026)},
  pages =	{45:1--45:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-418-5},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{367},
  editor =	{Ahn, Hee-Kap and Hoffmann, Michael and Nayyeri, Amir},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2026.45},
  URN =		{urn:nbn:de:0030-drops-258516},
  doi =		{10.4230/LIPIcs.SoCG.2026.45},
  annote =	{Keywords: Visibility, line segments, link distance, window partition, computation, implementation, robustness, scalability, exactness, CGAL}
}
Document
DOI: 10.4230/LIPIcs.FUN.2026.10
77 Shades of Grey

Authors: Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani

Published in: LIPIcs, Volume 366, 13th International Conference on Fun with Algorithms (FUN 2026)

Abstract
Bruce Wayne contacted us to help him develop a new surveillance technology for dark environments such as caves, using a swarm of Unmanned Aerial Vehicles (UAVs), called Batdroids. A Batdroid has no chirality, limited visibility, and a perfect clock to synchronize with the others. A Batdroid can produce 77 shades of grey in dark mode and four colors in light mode. In this paper, we propose two algorithms using three Batdroids to perpetually explore a finite 3D grid modeling a cave. The first algorithm operates in darkness, uses 77 shades of grey, and requires visibility range one. The second operates in light, uses four colors and visibility range two. We also prove that three is the optimal number of Batdroids required to solve Bruce Wayne’s challenge.
Cite as

Quentin Bramas, Stéphane Devismes, Anaïs Durand, Pascal Lafourcade, and Anissa Lamani. 77 Shades of Grey. In 13th International Conference on Fun with Algorithms (FUN 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 366, pp. 10:1-10:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{bramas_et_al:LIPIcs.FUN.2026.10,
  author =	{Bramas, Quentin and Devismes, St\'{e}phane and Durand, Ana\"{i}s and Lafourcade, Pascal and Lamani, Anissa},
  title =	{{77 Shades of Grey}},
  booktitle =	{13th International Conference on Fun with Algorithms (FUN 2026)},
  pages =	{10:1--10:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-417-8},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{366},
  editor =	{Iacono, John},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2026.10},
  URN =		{urn:nbn:de:0030-drops-257294},
  doi =		{10.4230/LIPIcs.FUN.2026.10},
  annote =	{Keywords: Mobile robots, grid exploration, perpetual exploration}
}
Document
DOI: 10.4230/LIPIcs.ITCS.2026.36
Beyond 2-Edge-Connectivity: Algorithms and Impossibility for Content-Oblivious Leader Election

Authors: Yi-Jun Chang, Lyuting Chen, and Haoran Zhou

Published in: LIPIcs, Volume 362, 17th Innovations in Theoretical Computer Science Conference (ITCS 2026)

Abstract
The content-oblivious model, introduced by Censor-Hillel, Cohen, Gelles, and Sela (PODC 2022; Distributed Computing 2023), captures an extremely weak form of communication where nodes can only send asynchronous, content-less pulses. They showed that in 2-edge-connected networks, any distributed algorithm can be simulated in the content-oblivious model, provided that a unique leader is designated a priori. Subsequent works of Frei, Gelles, Ghazy, and Nolin (DISC 2024) and Chalopin et al. (DISC 2025) developed content-oblivious leader election algorithms, first for unoriented rings and then for general 2-edge-connected graphs. These results establish that all graph problems are solvable in content-oblivious, 2-edge-connected networks. Much less is known about networks that are not 2-edge-connected. Censor-Hillel, Cohen, Gelles, and Sela showed that no non-constant function f(x,y) can be computed correctly by two parties using content-oblivious communication over a single edge, where one party holds x and the other holds y. This seemingly ruled out many natural graph problems on non-2-edge-connected graphs. In this work, we show that, with the knowledge of network topology G, leader election is possible in a wide range of graphs. Our main contributions are as follows: Impossibility: Graphs symmetric about an edge admit no randomized terminating leader election algorithm, even when nodes have unique identifiers and full knowledge of G. Leader election algorithms: Trees that are not symmetric about any edge admit a quiescently terminating leader election algorithm with topology knowledge, even in anonymous networks, using O(n²) messages, where n is the number of nodes. Moreover, even-diameter trees admit a terminating leader election given only the knowledge of the network diameter D = 2r, with message complexity O(nr). Necessity of topology knowledge: In the family of graphs 𝒢 = {P₃, P₅}, both the 3-path P₃ and the 5-path P₅ admit a quiescently terminating leader election if nodes know the topology exactly. However, if nodes only know that the underlying topology belongs to 𝒢, then terminating leader election is impossible.
Cite as

Yi-Jun Chang, Lyuting Chen, and Haoran Zhou. Beyond 2-Edge-Connectivity: Algorithms and Impossibility for Content-Oblivious Leader Election. In 17th Innovations in Theoretical Computer Science Conference (ITCS 2026). Leibniz International Proceedings in Informatics (LIPIcs), Volume 362, pp. 36:1-36:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2026)

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@InProceedings{chang_et_al:LIPIcs.ITCS.2026.36,
  author =	{Chang, Yi-Jun and Chen, Lyuting and Zhou, Haoran},
  title =	{{Beyond 2-Edge-Connectivity: Algorithms and Impossibility for Content-Oblivious Leader Election}},
  booktitle =	{17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
  pages =	{36:1--36:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-410-9},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{362},
  editor =	{Saraf, Shubhangi},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.36},
  URN =		{urn:nbn:de:0030-drops-253239},
  doi =		{10.4230/LIPIcs.ITCS.2026.36},
  annote =	{Keywords: Asynchronous model, fault tolerance, quiescent termination}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2025.7
Mobile Byzantine Agreement in a Trusted World

Authors: Bo Pan and Maria Potop-Butucaru

Published in: LIPIcs, Volume 361, 29th International Conference on Principles of Distributed Systems (OPODIS 2025)

Abstract
In this paper, we address the Byzantine Agreement problem in synchronous systems where Byzantine agents can move from process to process, corrupting their host. We focus on two representative models: Garay’s and Buhrman’s models. In Garay’s model, when a process has been left by the Byzantine agent, it enters a cured state, is aware of its condition, and can remain silent for a round to prevent the dissemination of incorrect information. In Buhrman’s model, a Byzantine agent moves together with the message. It has been shown that solving Byzantine Agreement requires at least 4t + 1 processes in Garay’s model, and at least 3t + 1 in Buhrman’s model. In this paper, we aim to increase the tolerance to mobile Byzantine agents by integrating a trusted counter abstraction into both models. This abstraction prevents nodes from equivocating. In the new models, we prove that at least 3t+1, respectively 2t+1 processors are needed to tolerate t mobile Byzantine agents. Furthermore, we propose novel Mobile Byzantine Agreement algorithms that match these new lower bounds for both Garay’s and Buhrman’s models, achieving agreement in 𝒪(n) synchronous rounds.
Cite as

Bo Pan and Maria Potop-Butucaru. Mobile Byzantine Agreement in a Trusted World. In 29th International Conference on Principles of Distributed Systems (OPODIS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 361, pp. 7:1-7:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{pan_et_al:LIPIcs.OPODIS.2025.7,
  author =	{Pan, Bo and Potop-Butucaru, Maria},
  title =	{{Mobile Byzantine Agreement in a Trusted World}},
  booktitle =	{29th International Conference on Principles of Distributed Systems (OPODIS 2025)},
  pages =	{7:1--7:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-409-3},
  ISSN =	{1868-8969},
  year =	{2026},
  volume =	{361},
  editor =	{Arusoaie, Andrei and Onica, Emanuel and Spear, Michael and Tucci-Piergiovanni, Sara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2025.7},
  URN =		{urn:nbn:de:0030-drops-251809},
  doi =		{10.4230/LIPIcs.OPODIS.2025.7},
  annote =	{Keywords: Byzantine Agreement, Mobile Faults, Trusted Abstractions}
}
Document
DOI: 10.4230/LIPIcs.DISC.2025.30
Team Formation and Applications

Authors: Yuval Emek, Shay Kutten, Ido Rafael, and Gadi Taubenfeld

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
A novel long-lived distributed problem, called Team Formation (TF), is introduced together with a message- and time-efficient randomized algorithm. The problem is defined over the asynchronous model with a complete communication graph, using bounded size messages, where a certain fraction of the nodes may experience a generalized, strictly stronger, version of initial failures. The goal of a TF algorithm is to assemble tokens injected by the environment, in a distributed manner, into teams of size σ, where σ is a parameter of the problem. The usefulness of TF is demonstrated by using it to derive efficient algorithms for many distributed problems. Specifically, we show that various (one-shot as well as long-lived) distributed problems reduce to TF. This includes well-known (and extensively studied) distributed problems such as several versions of leader election and threshold detection. For example, we are the first to break the linear message complexity bound for asynchronous implicit leader election. We also improve the time complexity of message-optimal algorithms for asynchronous explicit leader election. Other distributed problems that reduce to TF are new ones, including matching players in online gaming platforms, a generalization of gathering, constructing a perfect matching in an induced subgraph of the complete graph, and more. To complement our positive contribution, we establish a tight lower bound on the message complexity of TF algorithms.
Cite as

Yuval Emek, Shay Kutten, Ido Rafael, and Gadi Taubenfeld. Team Formation and Applications. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 30:1-30:25, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{emek_et_al:LIPIcs.DISC.2025.30,
  author =	{Emek, Yuval and Kutten, Shay and Rafael, Ido and Taubenfeld, Gadi},
  title =	{{Team Formation and Applications}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{30:1--30:25},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.30},
  URN =		{urn:nbn:de:0030-drops-248474},
  doi =		{10.4230/LIPIcs.DISC.2025.30},
  annote =	{Keywords: asynchronous message-passing, complete communication graph, initial failures, leader election, matching}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2025.56
Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers

Authors: Caterina Feletti, Paola Flocchini, Debasish Pattanayak, Giuseppe Prencipe, and Nicola Santoro

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
The Dancing problem requires a swarm of n autonomous mobile robots to form a sequence of patterns, aka perform a choreography. Existing work has proven that some crucial restrictions on choreographies and initial configurations (e.g., on repetitions of patterns, periodicity, symmetries, contractions/expansions) must hold so that the Dancing problem can be solved under certain robot models. Here, we prove that these necessary constraints can be dropped by considering the LUMI model (i.e., where robots are endowed with a light whose color can be chosen from a constant-size palette) under the quite unexplored sequential scheduler. We formalize the class of Universal Dancing problems which require a swarm of n robots starting from any initial configuration to perform a (periodic or finite) sequence of arbitrary patterns, only provided that each pattern consists of n vertices (including multiplicities). However, we prove that, to be solvable under LUMI, the length of the feasible choreographies is bounded by the compositions of n into the number of colors available to the robots. We provide an algorithm solving the Universal Dancing problem by exploiting the peculiar capability of sequential robots to implement a distributed counter mechanism. Even assuming non-rigid movements, our algorithm ensures spatial homogeneity of the performed choreography.
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Caterina Feletti, Paola Flocchini, Debasish Pattanayak, Giuseppe Prencipe, and Nicola Santoro. Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 56:1-56:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{feletti_et_al:LIPIcs.DISC.2025.56,
  author =	{Feletti, Caterina and Flocchini, Paola and Pattanayak, Debasish and Prencipe, Giuseppe and Santoro, Nicola},
  title =	{{Brief Announcement: Universal Dancing by Luminous Robots Under Sequential Schedulers}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{56:1--56:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.56},
  URN =		{urn:nbn:de:0030-drops-248724},
  doi =		{10.4230/LIPIcs.DISC.2025.56},
  annote =	{Keywords: Luminous Robots, Sequence of Patterns, Pattern Formation, Sequential Scheduler}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2025.57
Brief Announcement: The Virtue of Self-Consistency

Authors: Fabian Frei and Koichi Wada

Published in: LIPIcs, Volume 356, 39th International Symposium on Distributed Computing (DISC 2025)

Abstract
We show that self-consistency can be a crucial property for autonomous mobile robots. Specifically, we consider the task of gathering three robots, placed adversarially in distinct locations in the Euclidean plane, in a single point. We assume the natural scheduler RoundRobin, which activates the robots in turns. An activated robot perceives all robot locations in an adversarially scaled, rotated, and mirrored Cartesian coordinate system with itself at the origin and then moves wherever it wants. We show that this task cannot be solved in the default robot model (without any consistency guarantees and no multiplicity detection) but becomes feasible if we assume self-consistency (i.e., no changes between the different activations of the same robot) of either the unit length (i.e., no scaling) or the compass (i.e., no rotating) by providing explicit algorithms.
Cite as

Fabian Frei and Koichi Wada. Brief Announcement: The Virtue of Self-Consistency. In 39th International Symposium on Distributed Computing (DISC 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 356, pp. 57:1-57:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{frei_et_al:LIPIcs.DISC.2025.57,
  author =	{Frei, Fabian and Wada, Koichi},
  title =	{{Brief Announcement: The Virtue of Self-Consistency}},
  booktitle =	{39th International Symposium on Distributed Computing (DISC 2025)},
  pages =	{57:1--57:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-402-4},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{356},
  editor =	{Kowalski, Dariusz R.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2025.57},
  URN =		{urn:nbn:de:0030-drops-248737},
  doi =		{10.4230/LIPIcs.DISC.2025.57},
  annote =	{Keywords: Autonomous Mobile Robots, Distinct Gathering, Round Robin, Disorientation, Self-Consistency}
}
Document
DOI: 10.4230/LIPIcs.ESA.2025.28
Sliding Squares in Parallel

Authors: Hugo A. Akitaya, Sándor P. Fekete, Peter Kramer, Saba Molaei, Christian Rieck, Frederick Stock, and Tobias Wallner

Published in: LIPIcs, Volume 351, 33rd Annual European Symposium on Algorithms (ESA 2025)

Abstract
We consider algorithmic problems motivated by modular robotic reconfiguration in the sliding square model, in which we are given n square-shaped modules in a (labeled or unlabeled) start configuration and need to find a schedule of sliding moves to transform it into a desired goal configuration, maintaining connectivity of the configuration at all times. Recent work has aimed at minimizing the total number of moves, resulting in fully sequential schedules that can perform reconfiguration in 𝒪(n²) moves, or 𝒪(nP) for arrangements of bounding box perimeter size P. We provide first results in the sliding square model that exploit parallel motion, performing reconfiguration in worst-case optimal makespan of 𝒪(P). We also provide tight bounds on the complexity of the problem by showing that even deciding the possibility of reconfiguration within makespan 1 is NP-complete in the unlabeled case. In the labeled variant, we note that deciding the same for makespan 2 is NP-complete, while makespan 1 is straightforward.
Cite as

Hugo A. Akitaya, Sándor P. Fekete, Peter Kramer, Saba Molaei, Christian Rieck, Frederick Stock, and Tobias Wallner. Sliding Squares in Parallel. In 33rd Annual European Symposium on Algorithms (ESA 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 351, pp. 28:1-28:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{a.akitaya_et_al:LIPIcs.ESA.2025.28,
  author =	{A. Akitaya, Hugo and Fekete, S\'{a}ndor P. and Kramer, Peter and Molaei, Saba and Rieck, Christian and Stock, Frederick and Wallner, Tobias},
  title =	{{Sliding Squares in Parallel}},
  booktitle =	{33rd Annual European Symposium on Algorithms (ESA 2025)},
  pages =	{28:1--28:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-395-9},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{351},
  editor =	{Benoit, Anne and Kaplan, Haim and Wild, Sebastian and Herman, Grzegorz},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2025.28},
  URN =		{urn:nbn:de:0030-drops-244961},
  doi =		{10.4230/LIPIcs.ESA.2025.28},
  annote =	{Keywords: Sliding squares, parallel motion, reconfigurability, motion planning, multi-agent path finding, makespan, swarm robotics, computational geometry}
}
Document
RANDOM
DOI: 10.4230/LIPIcs.APPROX/RANDOM.2025.41
What Is the Minimum Number of Random Bits Required for Computability and Efficiency in Anonymous Networks?

Authors: Dariusz R. Kowalski, Piotr Krysta, and Shay Kutten

Published in: LIPIcs, Volume 353, Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2025)

Abstract
Angluin (STOC'80) and Yamashita and Kameda (PODC'88) show that some useful distributed tasks are impossible (for deterministic algorithms) in a general network if nodes do not possess unique identifiers. However, any task decidable in the non-distributed context, can be solved deterministically if the network has a unique leader. Alternatively, much research has been devoted to randomized distributed algorithms in anonymous networks. We present tight upper and lower bounds for the fundamental question: How much randomness is necessary and sufficient to solve Leader Election (LE) in anonymous networks, i.e., to transform an anonymous network into a non-anonymous one? We prove that at least one random bit per node is required in some cases. Surprisingly, a single random bit is also enough, for a total of n bits, where n is the number of nodes. However, the time complexity of our (total of) n random bits algorithm for general networks turned out to be impractically high. Hence, we also developed time-efficient algorithms for the very symmetric graphs of cliques and cycles, paying only an additional cost of o(n) random bits. The primary steps of our algorithms are of independent interest. At first glance, it seems that using one random bit per node, any algorithm can distinguish only two sets of nodes: those with 0 and those with 1. Our algorithms manage to partition the nodes into more than two sets with high probability. In some sense, they perform the task of a "distributed pseudorandom generator", for example, one of our algorithms turns n bits, one per node, into n unique (with high probability) numbers. Even though a complete graph looks very symmetric, the algorithms explore interesting asymmetries inherent in any n permutations (of n values each), if each describes the assignment (by the adversary) of ports in a node to edges leading to neighbors. Finally, we show how to transform any randomized algorithm that generates xn+o(n) random bits in total to one where each node generates at most x+1 bits. Our results apply to both synchronous and asynchronous networks.
Cite as

Dariusz R. Kowalski, Piotr Krysta, and Shay Kutten. What Is the Minimum Number of Random Bits Required for Computability and Efficiency in Anonymous Networks?. In Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 353, pp. 41:1-41:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kowalski_et_al:LIPIcs.APPROX/RANDOM.2025.41,
  author =	{Kowalski, Dariusz R. and Krysta, Piotr and Kutten, Shay},
  title =	{{What Is the Minimum Number of Random Bits Required for Computability and Efficiency in Anonymous Networks?}},
  booktitle =	{Approximation, Randomization, and Combinatorial Optimization. Algorithms and Techniques (APPROX/RANDOM 2025)},
  pages =	{41:1--41:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-397-3},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{353},
  editor =	{Ene, Alina and Chattopadhyay, Eshan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.APPROX/RANDOM.2025.41},
  URN =		{urn:nbn:de:0030-drops-244071},
  doi =		{10.4230/LIPIcs.APPROX/RANDOM.2025.41},
  annote =	{Keywords: Distributed computability, Anonymous Networks, Randomness, Leader Election}
}
Document
DOI: 10.4230/LIPIcs.WADS.2025.39
Sweeping a Domain with Line-Of-Sight Between Covisible Agents

Authors: Kien C. Huynh, Joseph S. B. Mitchell, and Valentin Polishchuk

Published in: LIPIcs, Volume 349, 19th International Symposium on Algorithms and Data Structures (WADS 2025)

Abstract
We consider sweeping a polygonal domain using variable-length segments whose endpoints can be considered to be mobile agents moving with bounded speeds; a point in the domain is swept when it belongs to one of the segments. The objective is to sweep the domain as quickly as possible. We show that the problem is NP-hard even in simple polygons and even for a single segment (two agents), and give constant-factor approximation algorithms, both for simple polygons and polygons with holes. Our approximations are obtained by introducing a new type of "window partition" of the polygon, which may find other applications. For domains with holes, our results are based on a non-trivial topological argument proving a surprising fact: a connected subset of the domain, whose points are swept but not directly touched by the agents, may contain at most one hole.
Cite as

Kien C. Huynh, Joseph S. B. Mitchell, and Valentin Polishchuk. Sweeping a Domain with Line-Of-Sight Between Covisible Agents. In 19th International Symposium on Algorithms and Data Structures (WADS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 349, pp. 39:1-39:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{huynh_et_al:LIPIcs.WADS.2025.39,
  author =	{Huynh, Kien C. and Mitchell, Joseph S. B. and Polishchuk, Valentin},
  title =	{{Sweeping a Domain with Line-Of-Sight Between Covisible Agents}},
  booktitle =	{19th International Symposium on Algorithms and Data Structures (WADS 2025)},
  pages =	{39:1--39:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-398-0},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{349},
  editor =	{Morin, Pat and Oh, Eunjin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.WADS.2025.39},
  URN =		{urn:nbn:de:0030-drops-242706},
  doi =		{10.4230/LIPIcs.WADS.2025.39},
  annote =	{Keywords: Polygon sweeping, collaborating agents, motion coordination, makespan optimization}
}
Document
Research
DOI: 10.4230/OASIcs.Grossi.8
Enumeration of Ordered Trees with Leaf Restrictions

Authors: Yasuaki Kobayashi, Dominik Köppl, Yasuko Matsui, Hirotaka Ono, Toshiki Saitoh, and Yushi Uno

Published in: OASIcs, Volume 132, From Strings to Graphs, and Back Again: A Festschrift for Roberto Grossi's 60th Birthday (2025)

Abstract
An α-ary tree for a constant α ≥ 2 is a rooted tree in which each node has at most α children. A node having no children is called a leaf. For a given rooted tree and a node v, the number of edges from the root to v is called the depth of v. We call a vector w = (w_1,w_2,…, w_d) of nonnegative integers an (α-ary) distribution if there is an α-ary tree T such that the number of leaves at each depth i ∈ [1..d] in T is w_i. Although not every vector of nonnegative integers is a distribution, a distribution can be associated with many α-ary trees. In this paper, we present an algorithm to enumerate all α-ary trees for a given distribution. Our algorithm reports the first tree in O(d + ∑_{i = 1}^d w_i) time, and then each subsequent α-ary tree in O(max_{i = 1}^d w_i) time by representing each tree as the difference from the previous one. The algorithm can be restricted to computing all trees that are full, i.e., trees whose nodes have exactly α or no children.
Cite as

Yasuaki Kobayashi, Dominik Köppl, Yasuko Matsui, Hirotaka Ono, Toshiki Saitoh, and Yushi Uno. Enumeration of Ordered Trees with Leaf Restrictions. In From Strings to Graphs, and Back Again: A Festschrift for Roberto Grossi's 60th Birthday. Open Access Series in Informatics (OASIcs), Volume 132, pp. 8:1-8:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{kobayashi_et_al:OASIcs.Grossi.8,
  author =	{Kobayashi, Yasuaki and K\"{o}ppl, Dominik and Matsui, Yasuko and Ono, Hirotaka and Saitoh, Toshiki and Uno, Yushi},
  title =	{{Enumeration of Ordered Trees with Leaf Restrictions}},
  booktitle =	{From Strings to Graphs, and Back Again: A Festschrift for Roberto Grossi's 60th Birthday},
  pages =	{8:1--8:19},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-391-1},
  ISSN =	{2190-6807},
  year =	{2025},
  volume =	{132},
  editor =	{Conte, Alessio and Marino, Andrea and Rosone, Giovanna and Vitter, Jeffrey Scott},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.Grossi.8},
  URN =		{urn:nbn:de:0030-drops-238077},
  doi =		{10.4230/OASIcs.Grossi.8},
  annote =	{Keywords: binary trees, ordered trees, rooted trees, enumeration algorithm, constant-time delay}
}
Document
Media Exposition
DOI: 10.4230/LIPIcs.SoCG.2025.85
Finding Shortest Reconfiguration Sequences for Modular Robots (Media Exposition)

Authors: UML Modular Robotics Group, Hugo A. Akitaya, Andrew Clements, Sam Downey, Jonathan Eisenbies, Soham Samanta, Gabriel Shahrouzi, and Frederick Stock

Published in: LIPIcs, Volume 332, 41st International Symposium on Computational Geometry (SoCG 2025)

Abstract
This paper introduces a set of tools built to help researchers design algorithms for modular robots. These tools can brute force solutions to specific reconfigurations, visualize movements of modular robots, and can be used to design specific configurations of robots. Multiple models of modular robots are supported, and can be added by users.
Cite as

UML Modular Robotics Group, Hugo A. Akitaya, Andrew Clements, Sam Downey, Jonathan Eisenbies, Soham Samanta, Gabriel Shahrouzi, and Frederick Stock. Finding Shortest Reconfiguration Sequences for Modular Robots (Media Exposition). In 41st International Symposium on Computational Geometry (SoCG 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 332, pp. 85:1-85:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{umlmodularroboticsgroup_et_al:LIPIcs.SoCG.2025.85,
  author =	{UML Modular Robotics Group and A. Akitaya, Hugo and Clements, Andrew and Downey, Sam and Eisenbies, Jonathan and Samanta, Soham and Shahrouzi, Gabriel and Stock, Frederick},
  title =	{{Finding Shortest Reconfiguration Sequences for Modular Robots}},
  booktitle =	{41st International Symposium on Computational Geometry (SoCG 2025)},
  pages =	{85:1--85:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-370-6},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{332},
  editor =	{Aichholzer, Oswin and Wang, Haitao},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2025.85},
  URN =		{urn:nbn:de:0030-drops-232371},
  doi =		{10.4230/LIPIcs.SoCG.2025.85},
  annote =	{Keywords: modular reconfigurable robots, sliding cube model, reconfiguration}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.SAND.2025.17
Brief Announcement: Broadcast via Mobile Agents in a Dynamic Network: Interplay of Graph Properties & Agents

Authors: William K. Moses Jr., Amanda Redlich, and Frederick Stock

Published in: LIPIcs, Volume 330, 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)

Abstract
In this paper, we revisit the problem of Broadcast, introduced by Das, Giachoudis, Luccio, and Markou [OPODIS, 2020], where k+1 agents are initially placed on an n node dynamic graph, where 1 agent has a message that must be broadcast to the remaining k ignorant agents. The original paper studied the relationship between the number of agents needed to solve the problem and the edge density of the graph. The paper presented strong evidence that edge density of a graph, or the number of redundant edges within the graph, may be the correct graph property to accurately differentiate whether k = o(n) agents (low edge density) or k = Ω(n) agents (high edge density) are needed to solve the problem. In this paper, we show that surprisingly, edge density is not in fact the differentiating property. The original paper presents graphs with edge density 1.1 ̅{6} that require Ω(n) agents, however, we construct graphs with edge density > 1.1 ̅{6} and develop an algorithm to solve the problem on those graphs using only o(n) agents. We further show that the relationship between edge density and number of agents is fairly weak by first constructing graphs with edge density tending to 1 from above that require Ω(n/f(n)) agents to solve, for any function f(n) → ∞ as n → ∞. We then construct an infinite family of graphs with edge density < ρ requiring exactly k ignorant agents to solve Broadcast, for any k > 0 and ρ > 1. Finally, we investigate different versions of connectivity as possible properties determining the number of agents. We show that edge connectivity is not related to the number of agents: it is possible for a graph to have low (constant) edge connectivity but require a high (linear) number of agents to solve Broadcast. More generally, for any arbitrary λ, we construct a family of graphs on n nodes with edge connectivity (n-1)/λ requiring exactly k = n - 2 λ + 1 agents. On the other hand, we show vertex connectivity can impact the required number of agents: for any graph with vertex connectivity ≥ 3 and minimum degree δ, k ≥ δ - 1 agents are required to solve Broadcast. Finally, we show that for any graph containing a certain type of bond with m edges, Broadcast is unsolvable when k ≤ m-2.
Cite as

William K. Moses Jr., Amanda Redlich, and Frederick Stock. Brief Announcement: Broadcast via Mobile Agents in a Dynamic Network: Interplay of Graph Properties & Agents. In 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 330, pp. 17:1-17:5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{mosesjr._et_al:LIPIcs.SAND.2025.17,
  author =	{Moses Jr., William K. and Redlich, Amanda and Stock, Frederick},
  title =	{{Brief Announcement: Broadcast via Mobile Agents in a Dynamic Network: Interplay of Graph Properties \& Agents}},
  booktitle =	{4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)},
  pages =	{17:1--17:5},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-368-3},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{330},
  editor =	{Meeks, Kitty and Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAND.2025.17},
  URN =		{urn:nbn:de:0030-drops-230708},
  doi =		{10.4230/LIPIcs.SAND.2025.17},
  annote =	{Keywords: Mobile agents, mobile robots, broadcast, dynamic graph, dynamic network}
}
Document
DOI: 10.4230/LIPIcs.SAND.2025.10
Fault Detection and Identification by Autonomous Mobile Robots

Authors: Stefano Clemente and Caterina Feletti

Published in: LIPIcs, Volume 330, 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)

Abstract
The Look-Compute-Move model (LCM) is adopted to study swarms of mobile robots that have to solve a given problem. Robots are generally assumed to be autonomous, indistinguishable, anonymous, homogeneous and to move on the Euclidean plane. Different LCM sub-models have been theorized to study different settings and their computational power. Notably, the literature has focused on four base models (i.e., OBLOT, FSTA, FCOM, LUMI) that differ in memory and communication capabilities, and in different synchronization modes (e.g., fully synchronous FSYNCH, semi-synchronous SSYNCH). In this paper, we consider fault-prone models where robots can suffer from crash faults: each robot may irremediably stop working after an unpredictable time. We study the general Fault Detection (FD) problem which is solved by a swarm if it correctly detects whether a faulty robot exists in the swarm. The Fault Identification (FI) problem additionally requires identifying which robots are faulty. We consider 12 LCM sub-models (OBLOT, FSTA, FCOM, LUMI, combined with FSYNCH, SSYNCH, and the round-robin RROBIN) and we study the (im)possibility of designing reliable procedures to solve FD or FI. In particular, we propose three distributed algorithms so that a swarm can collectively solve FD under the models LUMI^FSYNCH, FCOM^FSYNCH, and LUMI^RROBIN.
Cite as

Stefano Clemente and Caterina Feletti. Fault Detection and Identification by Autonomous Mobile Robots. In 4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 330, pp. 10:1-10:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{clemente_et_al:LIPIcs.SAND.2025.10,
  author =	{Clemente, Stefano and Feletti, Caterina},
  title =	{{Fault Detection and Identification by Autonomous Mobile Robots}},
  booktitle =	{4th Symposium on Algorithmic Foundations of Dynamic Networks (SAND 2025)},
  pages =	{10:1--10:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-368-3},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{330},
  editor =	{Meeks, Kitty and Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SAND.2025.10},
  URN =		{urn:nbn:de:0030-drops-230639},
  doi =		{10.4230/LIPIcs.SAND.2025.10},
  annote =	{Keywords: Autonomous mobile robots, Faulty robots, Look-Compute-Move, Fault detection, Fault identification, Round-robin}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2024.13
Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility

Authors: Raphael Gerlach, Sören von der Gracht, Christopher Hahn, Jonas Harbig, and Peter Kling

Published in: LIPIcs, Volume 324, 28th International Conference on Principles of Distributed Systems (OPODIS 2024)

Abstract
In the general pattern formation (GPF) problem, a swarm of simple autonomous, disoriented robots must form a given pattern. The robots' simplicity imply a strong limitation: When the initial configuration is rotationally symmetric, only patterns with a similar symmetry can be formed [Masafumi Yamashita and Ichiro Suzuki, 2010]. The only known algorithm to form large patterns with limited visibility and without memory requires the robots to start in a near-gathering (a swarm of constant diameter) [Christopher Hahn et al., 2024]. However, not only do we not know any near-gathering algorithm guaranteed to preserve symmetry but most natural gathering strategies trivially increase symmetries [Jannik Castenow et al., 2022]. Thus, we study near-gathering without changing the swarm’s rotational symmetry for disoriented, oblivious robots with limited visibility (the OBLOT-model, see [Paola Flocchini et al., 2019]). We introduce a technique based on the theory of dynamical systems to analyze how a given algorithm affects symmetry and provide sufficient conditions for symmetry preservation. Until now, it was unknown whether the considered OBLOT-model allows for any non-trivial algorithm that always preserves symmetry. Our first result shows that a variant of Go-To-The-Average always preserves symmetry but may sometimes lead to multiple, unconnected near-gathering clusters. Our second result is a symmetry-preserving near-gathering algorithm that works on swarms with a convex boundary (the outer boundary of the unit disc graph) and without "holes" (circles of diameter 1 inside the boundary without any robots).
Cite as

Raphael Gerlach, Sören von der Gracht, Christopher Hahn, Jonas Harbig, and Peter Kling. Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility. In 28th International Conference on Principles of Distributed Systems (OPODIS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 324, pp. 13:1-13:28, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{gerlach_et_al:LIPIcs.OPODIS.2024.13,
  author =	{Gerlach, Raphael and von der Gracht, S\"{o}ren and Hahn, Christopher and Harbig, Jonas and Kling, Peter},
  title =	{{Symmetry Preservation in Swarms of Oblivious Robots with Limited Visibility}},
  booktitle =	{28th International Conference on Principles of Distributed Systems (OPODIS 2024)},
  pages =	{13:1--13:28},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-360-7},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{324},
  editor =	{Bonomi, Silvia and Galletta, Letterio and Rivi\`{e}re, Etienne and Schiavoni, Valerio},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2024.13},
  URN =		{urn:nbn:de:0030-drops-225490},
  doi =		{10.4230/LIPIcs.OPODIS.2024.13},
  annote =	{Keywords: Swarm Algorithm, Swarm Robots, Distributed Algorithm, Pattern Formation, Limited Visibility, Oblivious}
}
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