73 Search Results for "Prencipe, Giuseppe"

Volume

LIPIcs, Volume 157

10th International Conference on Fun with Algorithms (FUN 2021)

FUN 2021, May 30 to June 1, 2021, Favignana Island, Sicily, Italy

Editors: Martin Farach-Colton, Giuseppe Prencipe, and Ryuhei Uehara

Volume

LIPIcs, Volume 100

9th International Conference on Fun with Algorithms (FUN 2018)

FUN 2018, June 13-15, 2018, La Maddalena, Italy

Editors: Hiro Ito, Stefano Leonardi, Linda Pagli, and Giuseppe Prencipe

Document
DOI: 10.4230/LIPIcs.DISC.2024.9
Freeze-Tag in L₁ Has Wake-Up Time Five with Linear Complexity

Authors: Nicolas Bonichon, Arnaud Casteigts, Cyril Gavoille, and Nicolas Hanusse

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
The Freeze-Tag Problem, introduced in Arkin et al. (SODA'02) consists of waking up a swarm of n robots, starting from a single active robot. In the basic geometric version, every robot is given coordinates in the plane. As soon as a robot is awakened, it can move towards inactive robots to wake them up. The goal is to minimize the makespan of the last robot, the makespan. Despite significant progress on the computational complexity of this problem and on approximation algorithms, the characterization of exact bounds on the makespan remains one of the main open questions. In this paper, we settle this question for the 𝓁₁-norm, showing that a makespan of at most 5r can always be achieved, where r is the maximum distance between the initial active robot and any sleeping robot. Moreover, a schedule achieving a makespan of at most 5r can be computed in time O(n). Both bounds, the time and the makespan are optimal. Our results also imply for the 𝓁₂-norm a new upper bound of 5√2r ≈ 7.07r on the makespan, improving the best known bound of (5+2√2+√5)r ≈ 10.06r. Along the way, we introduce new linear time wake-up strategies, that apply to any norm and show that an optimal bound on the makespan can always be achieved by a schedule computable in linear time.
Cite as

Nicolas Bonichon, Arnaud Casteigts, Cyril Gavoille, and Nicolas Hanusse. Freeze-Tag in L₁ Has Wake-Up Time Five with Linear Complexity. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 9:1-9:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{bonichon_et_al:LIPIcs.DISC.2024.9,
  author =	{Bonichon, Nicolas and Casteigts, Arnaud and Gavoille, Cyril and Hanusse, Nicolas},
  title =	{{Freeze-Tag in L₁ Has Wake-Up Time Five with Linear Complexity}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{9:1--9:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.9},
  URN =		{urn:nbn:de:0030-drops-212356},
  doi =		{10.4230/LIPIcs.DISC.2024.9},
  annote =	{Keywords: freeze-tag problem, metric, algorithm}
}
Document
DOI: 10.4230/LIPIcs.DISC.2024.17
Breaking Through the Ω(n)-Space Barrier: Population Protocols Decide Double-Exponential Thresholds

Authors: Philipp Czerner

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
Population protocols are a model of distributed computation in which finite-state agents interact randomly in pairs. A protocol decides for any initial configuration whether it satisfies a fixed property, specified as a predicate on the set of configurations. A family of protocols deciding predicates φ_n is succinct if it uses 𝒪(|φ_n|) states, where φ_n is encoded as quantifier-free Presburger formula with coefficients in binary. (All predicates decidable by population protocols can be encoded in this manner.) While it is known that succinct protocols exist for all predicates, it is open whether protocols with o(|φ_n|) states exist for any family of predicates φ_n. We answer this affirmatively, by constructing protocols with 𝒪(log|φ_n|) states for some family of threshold predicates φ_n(x) ⇔ x ≥ k_n, with k₁,k₂,... ∈ ℕ. (In other words, protocols with 𝒪(n) states that decide x ≥ k for a k ≥ 2^2ⁿ.) This matches a known lower bound. Moreover, our construction for threshold predicates is the first that is not 1-aware, and it is almost self-stabilising.
Cite as

Philipp Czerner. Breaking Through the Ω(n)-Space Barrier: Population Protocols Decide Double-Exponential Thresholds. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 17:1-17:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{czerner:LIPIcs.DISC.2024.17,
  author =	{Czerner, Philipp},
  title =	{{Breaking Through the \Omega(n)-Space Barrier: Population Protocols Decide Double-Exponential Thresholds}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{17:1--17:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.17},
  URN =		{urn:nbn:de:0030-drops-212438},
  doi =		{10.4230/LIPIcs.DISC.2024.17},
  annote =	{Keywords: Distributed computing, population protocols, state complexity}
}
Document
DOI: 10.4230/LIPIcs.DISC.2024.35
Memory Lower Bounds and Impossibility Results for Anonymous Dynamic Broadcast

Authors: Garrett Parzych and Joshua J. Daymude

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
Broadcast is a ubiquitous distributed computing problem that underpins many other system tasks. In static, connected networks, it was recently shown that broadcast is solvable without any node memory and only constant-size messages in worst-case asymptotically optimal time (Hussak and Trehan, PODC'19/STACS'20/DC'23). In the dynamic setting of adversarial topology changes, however, existing algorithms rely on identifiers, port labels, or polynomial memory to solve broadcast and compute functions over node inputs. We investigate space-efficient, terminating broadcast algorithms for anonymous, synchronous, 1-interval connected dynamic networks and introduce the first memory lower bounds in this setting. Specifically, we prove that broadcast with termination detection is impossible for idle-start algorithms (where only the broadcaster can initially send messages) and otherwise requires Ω(log n) memory per node, where n is the number of nodes in the network. Even if the termination condition is relaxed to stabilizing termination (eventually no additional messages are sent), we show that any idle-start algorithm must use ω(1) memory per node, separating the static and dynamic settings for anonymous broadcast. This lower bound is not far from optimal, as we present an algorithm that solves broadcast with stabilizing termination using 𝒪(log n) memory per node in worst-case asymptotically optimal time. In sum, these results reveal the necessity of non-constant memory for nontrivial terminating computation in anonymous dynamic networks.
Cite as

Garrett Parzych and Joshua J. Daymude. Memory Lower Bounds and Impossibility Results for Anonymous Dynamic Broadcast. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 35:1-35:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{parzych_et_al:LIPIcs.DISC.2024.35,
  author =	{Parzych, Garrett and Daymude, Joshua J.},
  title =	{{Memory Lower Bounds and Impossibility Results for Anonymous Dynamic Broadcast}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{35:1--35:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.35},
  URN =		{urn:nbn:de:0030-drops-212615},
  doi =		{10.4230/LIPIcs.DISC.2024.35},
  annote =	{Keywords: Dynamic networks, anonymity, broadcast, space complexity, lower bounds, termination detection, stabilizing termination}
}
Document
DOI: 10.4230/LIPIcs.DISC.2024.39
The Power of Abstract MAC Layer: A Fault-Tolerance Perspective

Authors: Qinzi Zhang and Lewis Tseng

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
This paper studies the power of the "abstract MAC layer" model in a single-hop asynchronous network. The model captures primitive properties of modern wireless MAC protocols. In this model, Newport [PODC '14] proves that it is impossible to achieve deterministic consensus when nodes may crash. Subsequently, Newport and Robinson [DISC '18] present randomized consensus algorithms that terminate with O(n³ log n) expected broadcasts in a system of n nodes. We are not aware of any results on other fault-tolerant distributed tasks in this model. We first study the computability aspect of the abstract MAC layer. We present a wait-free algorithm that implements an atomic register. Furthermore, we show that in general, k-set consensus is impossible. Second, we aim to minimize storage complexity. Existing algorithms require Ω(n log n) bits. We propose two wait-free approximate consensus and two wait-free randomized binary consensus algorithms that only need constant storage complexity (except for the phase index). One randomized algorithm terminates with O(n log n) expected broadcasts. All our algorithms are anonymous, meaning that at the algorithm level, nodes do not need to have a unique identifier.
Cite as

Qinzi Zhang and Lewis Tseng. The Power of Abstract MAC Layer: A Fault-Tolerance Perspective. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 39:1-39:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{zhang_et_al:LIPIcs.DISC.2024.39,
  author =	{Zhang, Qinzi and Tseng, Lewis},
  title =	{{The Power of Abstract MAC Layer: A Fault-Tolerance Perspective}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{39:1--39:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.39},
  URN =		{urn:nbn:de:0030-drops-212677},
  doi =		{10.4230/LIPIcs.DISC.2024.39},
  annote =	{Keywords: Abstract MAC Layer, Computation Power, Consensus}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.46
Brief Announcement: Optimal Uniform Circle Formation by Asynchronous Luminous Robots

Authors: Caterina Feletti, Debasish Pattanayak, and Gokarna Sharma

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
We study the Uniform Circle Formation (UCF) problem for a swarm of n autonomous mobile robots operating in Look-Compute-Move (LCM) cycles on the Euclidean plane. We assume our robots are luminous, i.e. equipped with a persistent light that can assume a color chosen from a fixed palette, and opaque, i.e. not able to see beyond a collinear robot. Robots are said to collide if they share positions or their paths intersect within concurrent LCM cycles. To solve UCF, a swarm of n robots must autonomously arrange themselves so that each robot occupies a vertex of the same regular n-gon not fixed in advance. In terms of efficiency, the goal is to design an algorithm that optimizes (or provides a tradeoff between) two fundamental performance metrics: (i) the execution time and (ii) the size of the color palette. In this paper, we develop a deterministic algorithm solving UCF avoiding collisions in O(1)-time with O(1) colors under the asynchronous scheduler, which is asymptotically optimal with respect to both time and number of colors used, the first such result. Furthermore, the algorithm proposed here minimizes for the first time what we call the computational SEC, i.e. the smallest circular area where robots operate throughout the whole algorithm.
Cite as

Caterina Feletti, Debasish Pattanayak, and Gokarna Sharma. Brief Announcement: Optimal Uniform Circle Formation by Asynchronous Luminous Robots. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 46:1-46:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{feletti_et_al:LIPIcs.DISC.2024.46,
  author =	{Feletti, Caterina and Pattanayak, Debasish and Sharma, Gokarna},
  title =	{{Brief Announcement: Optimal Uniform Circle Formation by Asynchronous Luminous Robots}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{46:1--46:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.46},
  URN =		{urn:nbn:de:0030-drops-212748},
  doi =		{10.4230/LIPIcs.DISC.2024.46},
  annote =	{Keywords: Uniform Circle Formation, Robots with Lights, Autonomous Robots, Rank Encoding, Time and Color Complexities, Computational SEC}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.48
Brief Announcement: Distinct Gathering Under Round Robin

Authors: Fabian Frei and Koichi Wada

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
We resolve one of the longest-standing questions about autonomous mobile robots in a surprising way. Distinct Gathering is the fundamental cooperation task of letting robots, initially scattered across the plane in distinct locations, gather in an arbitrary single point. The scheduler Round Robin cyclically activates the robots one by one in a fixed order. When activated, a robot perceives all robot locations and moves wherever it wants based only on this information. For n = 2 robots, the task is trivial. What happens for n ≥ 3 has remained an open problem for decades by now. The established conjecture declares the task to be impossible in this case. We prove that it is indeed impossible for n = 3 but, to great surprise, possible again for any n ≥ 4. We go beyond the standard requirements by providing a very robust algorithm that does not require any consistency or self-consistency for the local Cartesian maps perceived by the robots and works even for non-rigid movement, that is, if robots may be unpredictably stopped and deactivated during a movement.
Cite as

Fabian Frei and Koichi Wada. Brief Announcement: Distinct Gathering Under Round Robin. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 48:1-48:8, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{frei_et_al:LIPIcs.DISC.2024.48,
  author =	{Frei, Fabian and Wada, Koichi},
  title =	{{Brief Announcement: Distinct Gathering Under Round Robin}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{48:1--48:8},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.48},
  URN =		{urn:nbn:de:0030-drops-212768},
  doi =		{10.4230/LIPIcs.DISC.2024.48},
  annote =	{Keywords: Autonomous mobile robots, Distinct Gathering, Round Robin}
}
Document
DOI: 10.4230/LIPIcs.SEA.2024.2
Engineering Zuffix Arrays

Authors: Paolo Boldi, Stefano Marchini, and Sebastiano Vigna

Published in: LIPIcs, Volume 301, 22nd International Symposium on Experimental Algorithms (SEA 2024)

Abstract
Searching patterns in long strings is a classical algorithmic problem with countless practical applications. Suffix trees and suffix arrays (and their variants) are a long-established solution that yields linear-time search (in the size of the pattern). In [Paolo Boldi and Sebastiano Vigna, 2018] it is shown that a z-map gadget can be attached to (enhanced) suffix arrays to improve their theoretical query time, obtaining a data structure called zuffix array. The main contribution of this paper is to show that a carefully engineered implementation of the z-map gadget does provide significant speedups with respect to enhanced suffix arrays on real-world datasets, albeit doubling the required space. In particular, for large alphabets we observe a sevenfold improvement in query time with respect to enhanced suffix arrays; even in the worst case (small alphabets), the query time is almost halved. Thus, zuffix arrays provide a very interesting new point in the space-time tradeoff spectrum.
Cite as

Paolo Boldi, Stefano Marchini, and Sebastiano Vigna. Engineering Zuffix Arrays. In 22nd International Symposium on Experimental Algorithms (SEA 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 301, pp. 2:1-2:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{boldi_et_al:LIPIcs.SEA.2024.2,
  author =	{Boldi, Paolo and Marchini, Stefano and Vigna, Sebastiano},
  title =	{{Engineering Zuffix Arrays}},
  booktitle =	{22nd International Symposium on Experimental Algorithms (SEA 2024)},
  pages =	{2:1--2:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-325-6},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{301},
  editor =	{Liberti, Leo},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SEA.2024.2},
  URN =		{urn:nbn:de:0030-drops-203677},
  doi =		{10.4230/LIPIcs.SEA.2024.2},
  annote =	{Keywords: Suffix trees, suffix arrays, z-fast tries}
}
Document
Track A: Algorithms, Complexity and Games
DOI: 10.4230/LIPIcs.ICALP.2024.55
Exploiting Automorphisms of Temporal Graphs for Fast Exploration and Rendezvous

Authors: Konstantinos Dogeas, Thomas Erlebach, Frank Kammer, Johannes Meintrup, and William K. Moses Jr.

Published in: LIPIcs, Volume 297, 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)

Abstract
Temporal graphs are dynamic graphs where the edge set can change in each time step, while the vertex set stays the same. Exploration of temporal graphs whose snapshot in each time step is a connected graph, called connected temporal graphs, has been widely studied. In this paper, we extend the concept of graph automorphisms from static graphs to temporal graphs and show for the first time that symmetries enable faster exploration: We prove that a connected temporal graph with n vertices and orbit number r (i.e., r is the number of automorphism orbits) can be explored in O(r n^{1+ε}) time steps, for any fixed ε > 0. For r = O(n^c) for constant c < 1, this is a significant improvement over the known tight worst-case bound of Θ(n²) time steps for arbitrary connected temporal graphs. We also give two lower bounds for temporal exploration, showing that Ω(n log n) time steps are required for some inputs with r = O(1) and that Ω(rn) time steps are required for some inputs for any r with 1 ≤ r ≤ n. Moreover, we show that the techniques we develop for fast exploration can be used to derive the following result for rendezvous: Two agents with different programs and without communication ability are placed by an adversary at arbitrary vertices and given full information about the connected temporal graph, except that they do not have consistent vertex labels. Then the two agents can meet at a common vertex after O(n^{1+ε}) time steps, for any constant ε > 0. For some connected temporal graphs with the orbit number being a constant, we also present a complementary lower bound of Ω(nlog n) time steps.
Cite as

Konstantinos Dogeas, Thomas Erlebach, Frank Kammer, Johannes Meintrup, and William K. Moses Jr.. Exploiting Automorphisms of Temporal Graphs for Fast Exploration and Rendezvous. In 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 297, pp. 55:1-55:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{dogeas_et_al:LIPIcs.ICALP.2024.55,
  author =	{Dogeas, Konstantinos and Erlebach, Thomas and Kammer, Frank and Meintrup, Johannes and Moses Jr., William K.},
  title =	{{Exploiting Automorphisms of Temporal Graphs for Fast Exploration and Rendezvous}},
  booktitle =	{51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)},
  pages =	{55:1--55:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-322-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{297},
  editor =	{Bringmann, Karl and Grohe, Martin and Puppis, Gabriele and Svensson, Ola},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2024.55},
  URN =		{urn:nbn:de:0030-drops-201989},
  doi =		{10.4230/LIPIcs.ICALP.2024.55},
  annote =	{Keywords: dynamic graphs, parameterized algorithms, algorithmic graph theory, graph automorphism, orbit number}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.33
Black Hole Search in Dynamic Rings: The Scattered Case

Authors: Giuseppe A. Di Luna, Paola Flocchini, Giuseppe Prencipe, and Nicola Santoro

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
In this paper we investigate the problem of searching for a black hole in a dynamic graph by a set of scattered agents (i.e., the agents start from arbitrary locations of the graph). The black hole is a node that silently destroys any agent visiting it. This kind of malicious node nicely models network failures such as a crashed host or a virus that erases the visiting agents. The black hole search problem is solved when at least one agent survives, and it has the entire map of the graph with the location of the black hole. We consider the case in which the underlining graph is a dynamic 1-interval connected ring: a ring graph in which at each round at most one edge can be missing. We first show that the problem cannot be solved if the agents can only communicate by using a face-to-face mechanism: this holds for any set of agents of constant size, with respect to the size n of the ring. To circumvent this impossibility we consider agents equipped with movable pebbles that can be left on nodes as a form of communication with other agents. When pebbles are available, three agents can localize the black hole in O(n²) moves. We show that such a number of agents is optimal. We also show that the complexity is tight, that is Ω(n²) moves are required for any algorithm solving the problem with three agents, even with stronger communication mechanisms (e.g., a whiteboard on each node on which agents can write messages of unlimited size). To the best of our knowledge this is the first paper examining the problem of searching a black hole in a dynamic environment with scattered agents.
Cite as

Giuseppe A. Di Luna, Paola Flocchini, Giuseppe Prencipe, and Nicola Santoro. Black Hole Search in Dynamic Rings: The Scattered Case. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 33:1-33:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{diluna_et_al:LIPIcs.OPODIS.2023.33,
  author =	{Di Luna, Giuseppe A. and Flocchini, Paola and Prencipe, Giuseppe and Santoro, Nicola},
  title =	{{Black Hole Search in Dynamic Rings: The Scattered Case}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{33:1--33:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.33},
  URN =		{urn:nbn:de:0030-drops-195233},
  doi =		{10.4230/LIPIcs.OPODIS.2023.33},
  annote =	{Keywords: Black hole search, mobile agents, dynamic graph}
}
Document
Complete Volume
DOI: 10.4230/LIPIcs.FUN.2021
LIPIcs, Volume 157, FUN 2021, Complete Volume

Authors: Martin Farach-Colton, Giuseppe Prencipe, and Ryuhei Uehara

Published in: LIPIcs, Volume 157, 10th International Conference on Fun with Algorithms (FUN 2021) (2020)

Abstract
LIPIcs, Volume 157, FUN 2021, Complete Volume
Cite as

10th International Conference on Fun with Algorithms (FUN 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 157, pp. 1-416, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@Proceedings{farachcolton_et_al:LIPIcs.FUN.2021,
  title =	{{LIPIcs, Volume 157, FUN 2021, Complete Volume}},
  booktitle =	{10th International Conference on Fun with Algorithms (FUN 2021)},
  pages =	{1--416},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-145-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{157},
  editor =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2021},
  URN =		{urn:nbn:de:0030-drops-127602},
  doi =		{10.4230/LIPIcs.FUN.2021},
  annote =	{Keywords: LIPIcs, Volume 157, FUN 2021, Complete Volume}
}
Document
Front Matter
DOI: 10.4230/LIPIcs.FUN.2021.0
Front Matter, Table of Contents, Preface, Conference Organization

Authors: Martin Farach-Colton, Giuseppe Prencipe, and Ryuhei Uehara

Published in: LIPIcs, Volume 157, 10th International Conference on Fun with Algorithms (FUN 2021) (2020)

Abstract
Front Matter, Table of Contents, Preface, Conference Organization
Cite as

10th International Conference on Fun with Algorithms (FUN 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 157, pp. 0:i-0:xvi, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{farachcolton_et_al:LIPIcs.FUN.2021.0,
  author =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  title =	{{Front Matter, Table of Contents, Preface, Conference Organization}},
  booktitle =	{10th International Conference on Fun with Algorithms (FUN 2021)},
  pages =	{0:i--0:xvi},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-145-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{157},
  editor =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2021.0},
  URN =		{urn:nbn:de:0030-drops-127613},
  doi =		{10.4230/LIPIcs.FUN.2021.0},
  annote =	{Keywords: Front Matter, Table of Contents, Preface, Conference Organization}
}
Document
DOI: 10.4230/LIPIcs.FUN.2021.1
Tatamibari Is NP-Complete

Authors: Aviv Adler, Jeffrey Bosboom, Erik D. Demaine, Martin L. Demaine, Quanquan C. Liu, and Jayson Lynch

Published in: LIPIcs, Volume 157, 10th International Conference on Fun with Algorithms (FUN 2021) (2020)

Abstract
In the Nikoli pencil-and-paper game Tatamibari, a puzzle consists of an m x n grid of cells, where each cell possibly contains a clue among ⊞, ⊟, ◫. The goal is to partition the grid into disjoint rectangles, where every rectangle contains exactly one clue, rectangles containing ⊞ are square, rectangles containing ⊟ are strictly longer horizontally than vertically, rectangles containing ◫ are strictly longer vertically than horizontally, and no four rectangles share a corner. We prove this puzzle NP-complete, establishing a Nikoli gap of 16 years. Along the way, we introduce a gadget framework for proving hardness of similar puzzles involving area coverage, and show that it applies to an existing NP-hardness proof for Spiral Galaxies. We also present a mathematical puzzle font for Tatamibari.
Cite as

Aviv Adler, Jeffrey Bosboom, Erik D. Demaine, Martin L. Demaine, Quanquan C. Liu, and Jayson Lynch. Tatamibari Is NP-Complete. In 10th International Conference on Fun with Algorithms (FUN 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 157, pp. 1:1-1:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{adler_et_al:LIPIcs.FUN.2021.1,
  author =	{Adler, Aviv and Bosboom, Jeffrey and Demaine, Erik D. and Demaine, Martin L. and Liu, Quanquan C. and Lynch, Jayson},
  title =	{{Tatamibari Is NP-Complete}},
  booktitle =	{10th International Conference on Fun with Algorithms (FUN 2021)},
  pages =	{1:1--1:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-145-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{157},
  editor =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2021.1},
  URN =		{urn:nbn:de:0030-drops-127624},
  doi =		{10.4230/LIPIcs.FUN.2021.1},
  annote =	{Keywords: Nikoli puzzles, NP-hardness, rectangle covering}
}
Document
DOI: 10.4230/LIPIcs.FUN.2021.2
Collaborative Procrastination

Authors: Aris Anagnostopoulos, Aristides Gionis, and Nikos Parotsidis

Published in: LIPIcs, Volume 157, 10th International Conference on Fun with Algorithms (FUN 2021) (2020)

Abstract
The problem of inconsistent planning in decision making, which leads to undesirable effects such as procrastination, has been studied in the behavioral-economics literature, and more recently in the context of computational behavioral models. Individuals, however, do not function in isolation, and successful projects most often rely on team work. Team performance does not depend only on the skills of the individual team members, but also on other collective factors, such as team spirit and cohesion. It is not an uncommon situation (for instance, experienced by the authors while working on this paper) that a hard-working individual has the capacity to give a good example to her team-mates and motivate them to work harder. In this paper we adopt the model of Kleinberg and Oren (EC'14) on time-inconsistent planning, and extend it to account for the influence of procrastination within the members of a team. Our first contribution is to model collaborative work so that the relative progress of the team members, with respect to their respective subtasks, motivates (or discourages) them to work harder. We compare the total cost of completing a team project when the team members communicate with each other about their progress, with the corresponding cost when they work in isolation. Our main result is a tight bound on the ratio of these two costs, under mild assumptions. We also show that communication can either increase or decrease the total cost. We also consider the problem of assigning subtasks to team members, with the objective of minimizing the negative effects of collaborative procrastination. We show that whereas a simple problem of forming teams of two members can be solved in polynomial time, the problem of assigning n tasks to n agents is NP-hard.
Cite as

Aris Anagnostopoulos, Aristides Gionis, and Nikos Parotsidis. Collaborative Procrastination. In 10th International Conference on Fun with Algorithms (FUN 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 157, pp. 2:1-2:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{anagnostopoulos_et_al:LIPIcs.FUN.2021.2,
  author =	{Anagnostopoulos, Aris and Gionis, Aristides and Parotsidis, Nikos},
  title =	{{Collaborative Procrastination}},
  booktitle =	{10th International Conference on Fun with Algorithms (FUN 2021)},
  pages =	{2:1--2:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-145-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{157},
  editor =	{Farach-Colton, Martin and Prencipe, Giuseppe and Uehara, Ryuhei},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FUN.2021.2},
  URN =		{urn:nbn:de:0030-drops-127634},
  doi =		{10.4230/LIPIcs.FUN.2021.2},
  annote =	{Keywords: time-inconsistent planning, computational behavioral science, collaborative work, collaborative environments}
}
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