Theory and Practical Applications of Treewidth Tom C

Total Page:16

File Type:pdf, Size:1020Kb

Theory and Practical Applications of Treewidth Tom C Theory and Practical Applications of Treewidth Tom C. van der Zanden C. van Tom of Treewidth Applications Theory and Practical Theory and Practical Applications of Treewidth Tom C. van der Zanden Theory and Practical Applications of Treewidth Tom C. van der Zanden Tom C. van der Zanden Theory and Practical Applications of Treewidth ISBN: 978-90-393-7147-3 c Tom C. van der Zanden, Utrecht 2019 [email protected] www.tomvanderzanden.nl Cover design and printing: Drukkerij Haveka, Alblasserdam Theory and Practical Applications of Treewidth Theorie en Praktische Toepassingen van Treewidth (met een samenvatting in het Nederlands) Proefschrift ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof.dr. H.R.B.M. Kummeling, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op woensdag 26 juni 2019 des middags te 2.30 uur door Tom Cornelis van der Zanden geboren op 29 december 1992 te Nieuwegein Promotor: Prof. dr. H. L. Bodlaender i Acknowledgements The four years of my PhD have been an amazing adventure. Four years to develop new ideas and to explore the mathematical beauty of algorithms, to meet many new friends, and to visit conferences in wonderful and inspiring locations. First and foremost, I want to thank my advisor, Hans Bodlaender. I was very lucky to have Hans as an advisor: most of the supervision happened during the daily morning and afternoon coffee sessions, where small talk with colleagues was interspersed with occasional discussions about our research. Formal meetings were rare, but Hans was always available to discuss if I had something to ask. Hans provided helpful research directions, but also left me plenty of freedom to explore my own interests. My research would not have been possible without the input of many collaborators. Key among these is Sándor Kisfaludi-Bak, with whom I initiated collaboration during the Lorentz Center workshop Fixed-Parameter Computational Geometry in 2016. Sándor was my city guide during our joint two-week research visit to Dániel Marx at the MTA SZTAKI in Budapest. This visit, together with many days in Eindhoven and Utrecht spent in a small room with a whiteboard, culminated in no less than three papers. I cannot commend Sándor enough1: he is a very smart, talented and hard-working mathematician and moreover, a very humble and kind person. Another very important research visit was that to the Fukuoka Institute of Tech- nology in Japan in 2017. While this was also a very productive visit (resulting in papers on memory-efficient algorithms, Subgraph Isomorphism, k-Path Vertex Cover and minimal separators), it also resulted in personal growth: being able to spend three weeks immersed in Japanese culture was transformative, the experience that I got can simply not be had as a tourist. I want to say arigat¯ogozaimashita to all of my Japanese friends: Tesshu Hanaka, Eiji Miyano, Yota Otachi, Toshiki Saitoh, Hisao Tamaki, Ryuhei Uehara, Yushi Uno, Tsuyoshi Yagita and to the students at the Fukuoka Institute of Technology who invited me to their homes. To people who are not familiar with mathematics and computer science research, it might appear boring and dry. However, to me, it sometimes feels more like a thinly veiled excuse for having fun and an extension of my hobby in puzzles. In fact, my work together with Hans was initiated when I, during his Algorithms and Networks course, took a homework assignment on the puzzle game Bloxorz a bit too far. I have met many people who think alike at various International Puzzle Parties, Gathering for Gardner 10 and 13, the 2018 Fun with Algorithms Conference in Sardinia and the 2019 Bellairs Workshop on Computational Geometry in Barbados (certainly, the only thing better than having fun with mathematics is having fun with mathematics on a beautiful tropical island). I want to acknowledge all of the people that I met pursuing 1And Sándor tells me I shouldn’t. ii Acknowledgements my interest in recreational mathematics, puzzles and their design, and in particular Andrew Cormier, Martin and Erik Demaine, Oskar van Deventer, Bob Hearn, Marc van Kreveld, Jayson Lynch, Jonathan Schroyer, Joris van Tubergen, Siert Wijnia and many others. I also want to thank the Gathering for Gardner Foundation and the late Tom Rodgers for their support. Of course, not everything is fun and games (or at least, not the type of game that is fun to play). I want to thank Herbert Hamers for our collaboration on terrorist networks, which was initiated at Lunteren 2017. I am very happy Herbert was willing to take on this interdisciplinary challenge. I would like to thank the reading committee for critically evaluating this manuscript and offering valuable comments: Hajo Broersma, Alexander Grigoriev, Marc van Kreveld, Jan Arne Telle and Gerhard Woeginger. During the NETWORKS training weeks, visiting Eindhoven and at other conferences I had a lot of fun with my fellow PhD students and other colleagues: Tom Bannink, Julien Baste, Paul Bouman, Jan-Willem Buurlage, Mark de Berg, Huib Donkers, Lars Jaffke, Bart Jansen, Aleksandar Markovic, Jesper Nederlof, Tim Ophelders, Astrid Pieterse, Carolin Rehs, Jan Arne Telle, Abe Wits, Gerhard Woeginger and many, many others. Being able to interact with so many people, and especially getting to meet fellow PhDs in similar and different stages of their programme was very valuable to me. I want to say a special thank you to Astrid and Sándor, who have been good friends from the very beginning of our PhD programmes. Of course, there are also many wonderful and inspiring people at my home base of Utrecht. My interest in algorithms was first sparked by taking part in programming contests, together with my teammates Bas te Kolste, Harry Smit and coaches Jeroen Bransen and Bas den Heijer. I want to thank Gerard Tel for teaching a wonderful introduction to algorithms class and inspiring me in the area of teaching. I have been a student assistant for many of Gerard’s classes, and I appreciate the opportunities he gave me to substitute during classroom lectures and to experiment with developing practical assignments. I want to thank Erik Jan van Leeuwen for our collaboration while teaching the algorithms course, Johan van Rooij for advising me on job searching inside and out of academia, Tomas Klos for occasionally reminding me to take the train instead of flying, Han Hoogeveen for our work on data mining and flower power, Jacco Bikker for discussions on GPU programming, Linda van der Gaag for making sure Hans stayed on top of his negotiating skills, Marjan van den Akker, Rob Bisseling, Janneke Bolt, Anneke Bonsma, Wouter ten Bosch, Cassio de Campos, Gunther Cornelissen, Federico D’Ambrosio, Marcell van Geest, Roland Geraerts, Jurriaan Hage, Ivor van der Hoog, Jan van Leeuwen, Till Miltzow, Thijs van Ommen, Silja Renooij, Edith Stap, Dirk Thierens, Sjoerd Timmer, Jérôme Urhausen, Marinus Veldhorst, Peter de Waal and Jordi Vermeulen. I would also like to thank the students who I shared the joy of many moments of learning and discovery with. I would like to thank my long-term office mates, Roel van den Broek, Nils Donselaar and Marieke van der Wegen, for the good times we shared inside and out of the office and at conferences in Vienna, Lunteren, Helsinki, Nový Smokovec and Heeze. Finally, I would like to thank my parents Hans and Loes, and several good friends and people who meant a lot for me: Elsie, Gerrit, Irene, Marrie, Cor, Daan, Jacco – thank you all very much. iii Contents 1. Introduction 1 1.1. Hard Problems . .2 1.2. The Exponential Time Hypothesis . .4 1.3. Graph Separators and Treewidth . .4 1.4. The Square Root Phenomenon in Planar Graphs . .7 1.5. Graph Embedding Problems . .8 1.6. Problems in Geometric Intersection Graphs . .9 1.7. Treewidth in Practice . 11 1.8. Published Papers . 12 2. Preliminaries 15 2.1. Basic Notations and Definitions . 15 2.2. Tree Decompositions . 16 2.3. Dynamic Programming on Tree Decompositions . 17 I Graph Embedding Problems 21 3. Algorithms 23 3.1. Introduction . 23 3.2. An Algorithm for Subgraph Isomorphism . 25 3.3. Reducing the Number of Partial Solutions Using Isomorphism Tests 28 3.4. Bounding the Number of Non-Isomorphic Partial Solutions . 29 3.5. Graph Minors and Induced Problem Variants . 31 3.6. Topological Minor . 35 3.7. Conclusions . 38 4. Lower Bounds 41 4.1. Introduction . 41 4.2. Additional Notation . 43 4.3. String Crafting and Orthogonal Vector Crafting . 43 4.4. Lower Bounds for Graph Embedding Problems . 47 4.5. Tree and Path Decompositions with Few Bags . 49 4.6. Intervalizing Coloured Graphs . 51 4.7. Conclusions . 59 iv Contents 5. Intermezzo: Polyomino Packing 61 5.1. Introduction . 61 5.2. Lower Bounds . 62 5.3. Algorithms . 67 5.4. Conclusions . 70 II Problems in Geometric Intersection Graphs 73 6. Problems in Geometric Intersection Graphs 75 6.1. Introduction . 75 6.2. Separators for Arbitrarily-Sized Fat Objects . 77 6.3. An Algorithmic Framework for Similarly-Sized Fat Objects . 81 6.4. Basic Algorithmic Applications . 84 6.5. Application of the Rank-Based Approach . 87 6.6. Conclusions . 90 III Practical Applications of Treewidth 91 7. Computing Tree Decompositions on the GPU 93 7.1. Introduction . 93 7.2. Additional Definitions . 95 7.3. The Algorithm . 96 7.3.1. Computing Treewidth . 96 7.3.2. Duplicate Elimination using Bloom Filters . 97 7.3.3. Minor-Min-Width . 98 7.4. Experiments . 99 7.4.1. Instances . 99 7.4.2. General Benchmark . 99 7.4.3. Work Size and Global v.s. Shared Memory . 101 7.4.4.
Recommended publications
  • Generating Single and Multiple Cooperative Heuristics for the One Dimensional Bin Packing Problem Using a Single Node Genetic Programming Island Model
    Generating Single and Multiple Cooperative Heuristics for the One Dimensional Bin Packing Problem Using a Single Node Genetic Programming Island Model Kevin Sim Emma Hart Institute for Informatics and Digital Innovation Institute for Informatics and Digital Innovation Edinburgh Napier University Edinburgh Napier University Edinburgh, Scotland, UK Edinburgh, Scotland, UK [email protected] [email protected] ABSTRACT exhibit superior performance than similar human designed Novel deterministic heuristics are generated using Single Node heuristics and can be used to produce collections of heuris- Genetic Programming for application to the One Dimen- tics that collectively maximise the potential of selective HH. sional Bin Packing Problem. First a single deterministic The papers contribution is two fold. Single heuristics ca- heuristic was evolved that minimised the total number of pable of outperforming a range of well researched deter- bins used when applied to a set of 685 training instances. ministic heuristics are generated by combining features ex- Following this, a set of heuristics were evolved using a form tracted from those heuristics. Secondly an island model[19] of cooperative co-evolution that collectively minimise the is adapted to use multiple SNGP implementations to gener- number of bins used across the same set of problems. Re- ate diverse sets of heuristics which collectively outperform sults on an unseen test set comprising a further 685 prob- any of the single heuristics when used in isolation. Both ap- lem instances show that the single evolved heuristic out- proaches are trained and evaluated using equal divisions of a performs existing deterministic heuristics described in the large set of 1370 benchmark problem instances sourced from literature.
    [Show full text]
  • 13. Mathematics University of Central Oklahoma
    Southwestern Oklahoma State University SWOSU Digital Commons Oklahoma Research Day Abstracts 2013 Oklahoma Research Day Jan 10th, 12:00 AM 13. Mathematics University of Central Oklahoma Follow this and additional works at: https://dc.swosu.edu/ordabstracts Part of the Animal Sciences Commons, Biology Commons, Chemistry Commons, Computer Sciences Commons, Environmental Sciences Commons, Mathematics Commons, and the Physics Commons University of Central Oklahoma, "13. Mathematics" (2013). Oklahoma Research Day Abstracts. 12. https://dc.swosu.edu/ordabstracts/2013oklahomaresearchday/mathematicsandscience/12 This Event is brought to you for free and open access by the Oklahoma Research Day at SWOSU Digital Commons. It has been accepted for inclusion in Oklahoma Research Day Abstracts by an authorized administrator of SWOSU Digital Commons. An ADA compliant document is available upon request. For more information, please contact [email protected]. Abstracts from the 2013 Oklahoma Research Day Held at the University of Central Oklahoma 05. Mathematics and Science 13. Mathematics 05.13.01 A simplified proof of the Kantorovich theorem for solving equations using scalar telescopic series Ioannis Argyros, Cameron University The Kantorovich theorem is an important tool in Mathematical Analysis for solving nonlinear equations in abstract spaces by approximating a locally unique solution using the popular Newton-Kantorovich method.Many proofs have been given for this theorem using techniques such as the contraction mapping principle,majorizing sequences, recurrent functions and other techniques.These methods are rather long,complicated and not very easy to understand in general by undergraduate students.In the present paper we present a proof using simple telescopic series studied first in a Calculus II class.
    [Show full text]
  • Lipics-WABI-2021-7.Pdf (2
    Tree Diet: Reducing the Treewidth to Unlock FPT Algorithms in RNA Bioinformatics Bertrand Marchand # LIX CNRS UMR 7161, Ecole Polytechnique, Institut Polytechnique de Paris, Palaiseau, France LIGM, CNRS, Univ Gustave Eiffel, F77454 Marne-la-vallée, France Yann Ponty1 # LIX CNRS UMR 7161, Ecole Polytechnique, Institut Polytechnique de Paris, Palaiseau, France Laurent Bulteau1 # LIGM, CNRS, Univ Gustave Eiffel, F77454 Marne-la-vallée, France Abstract Hard graph problems are ubiquitous in Bioinformatics, inspiring the design of specialized Fixed- Parameter Tractable algorithms, many of which rely on a combination of tree-decomposition and dynamic programming. The time/space complexities of such approaches hinge critically on low values for the treewidth tw of the input graph. In order to extend their scope of applicability, we introduce the Tree-Diet problem, i.e. the removal of a minimal set of edges such that a given tree-decomposition can be slimmed down to a prescribed treewidth tw′. Our rationale is that the time gained thanks to a smaller treewidth in a parameterized algorithm compensates the extra post-processing needed to take deleted edges into account. Our core result is an FPT dynamic programming algorithm for Tree-Diet, using 2O(tw)n time and space. We complement this result with parameterized complexity lower-bounds for stronger variants (e.g., NP-hardness when tw′ or tw−tw′ is constant). We propose a prototype implementation for our approach which we apply on difficult instances of selected RNA-based problems: RNA design, sequence-structure alignment, and search of pseudoknotted RNAs in genomes, revealing very encouraging results. This work paves the way for a wider adoption of tree-decomposition-based algorithms in Bioinformatics.
    [Show full text]
  • Complexity and Exact Algorithms for Vertex Multicut in Interval and Bounded Treewidth Graphs 1
    Complexity and Exact Algorithms for Vertex Multicut in Interval and Bounded Treewidth Graphs 1 Jiong Guo a,∗ Falk H¨uffner a Erhan Kenar b Rolf Niedermeier a Johannes Uhlmann a aInstitut f¨ur Informatik, Friedrich-Schiller-Universit¨at Jena, Ernst-Abbe-Platz 2, D-07743 Jena, Germany bWilhelm-Schickard-Institut f¨ur Informatik, Universit¨at T¨ubingen, Sand 13, D-72076 T¨ubingen, Germany Abstract Multicut is a fundamental network communication and connectivity problem. It is defined as: given an undirected graph and a collection of pairs of terminal vertices, find a minimum set of edges or vertices whose removal disconnects each pair. We mainly focus on the case of removing vertices, where we distinguish between allowing or disallowing the removal of terminal vertices. Complementing and refining previous results from the literature, we provide several NP-completeness and (fixed- parameter) tractability results for restricted classes of graphs such as trees, interval graphs, and graphs of bounded treewidth. Key words: Combinatorial optimization, Complexity theory, NP-completeness, Dynamic programming, Graph theory, Parameterized complexity 1 Introduction Motivation and previous results. Multicut in graphs is a fundamental network design problem. It models questions concerning the reliability and ∗ Corresponding author. Tel.: +49 3641 9 46325; fax: +49 3641 9 46002 E-mail address: [email protected]. 1 An extended abstract of this work appears in the proceedings of the 32nd Interna- tional Conference on Current Trends in Theory and Practice of Computer Science (SOFSEM 2006) [19]. Now, in particular the proof of Theorem 5 has been much simplified. Preprint submitted to Elsevier Science 2 February 2007 robustness of computer and communication networks.
    [Show full text]
  • Three-Dimensional Bin-Packing Approaches, Issues, and Solutions
    Three Dimensional Bin-Packing Issues and Solutions Seth Sweep University of Minnesota, Morris [email protected] Abstract This paper reviews the three-dimensional version of the classic NP-hard bin-packing, optimization problem along with its theoretical relevance and practical importance. Also, new approximation solutions are introduced based on prior research. The three-dimensional bin-packing optimization problem concerns placing box-shaped objects of arbitrary size and number into a box-shaped, three-dimensional space efficiently. Approximation algorithms become a guide that attempts to place objects in the least amount of space and time. As a NP-hard problem, three-dimensional bin- packing holds much academic interest to computer scientists. However, this problem also has relevance in industrial settings such as shipping cargo and efficiently designing machinery with replaceable parts, such as automobiles. Industry relies on algorithms to provide good solutions to versions of this problem. This research project adapted common approaches to one-dimensional bin-packing, such as next fit and best fit, to three dimensions. Adaptation of these algorithms is possible by dividing the space of a bin. Then, by paying attention strictly to the width of each object, the one-dimensional approaches attempt to efficiently pack into the divided compartments of the original bin. Through focusing entirely on width, these divisions effectively become multiple one-dimensional bins. However, entirely disregarding the volume of the bin by ignoring height and depth may generate inefficient packings. As this paper details in more depth, generally cubical objects may pack well but exceptionally high or long objects leave large gaps of empty space unpacked.
    [Show full text]
  • Algorithmic Combinatorial Game Theory∗
    Playing Games with Algorithms: Algorithmic Combinatorial Game Theory∗ Erik D. Demaine† Robert A. Hearn‡ Abstract Combinatorial games lead to several interesting, clean problems in algorithms and complexity theory, many of which remain open. The purpose of this paper is to provide an overview of the area to encourage further research. In particular, we begin with general background in Combinatorial Game Theory, which analyzes ideal play in perfect-information games, and Constraint Logic, which provides a framework for showing hardness. Then we survey results about the complexity of determining ideal play in these games, and the related problems of solving puzzles, in terms of both polynomial-time algorithms and computational intractability results. Our review of background and survey of algorithmic results are by no means complete, but should serve as a useful primer. 1 Introduction Many classic games are known to be computationally intractable (assuming P 6= NP): one-player puzzles are often NP-complete (as in Minesweeper) or PSPACE-complete (as in Rush Hour), and two-player games are often PSPACE-complete (as in Othello) or EXPTIME-complete (as in Check- ers, Chess, and Go). Surprisingly, many seemingly simple puzzles and games are also hard. Other results are positive, proving that some games can be played optimally in polynomial time. In some cases, particularly with one-player puzzles, the computationally tractable games are still interesting for humans to play. We begin by reviewing some basics of Combinatorial Game Theory in Section 2, which gives tools for designing algorithms, followed by reviewing the relatively new theory of Constraint Logic in Section 3, which gives tools for proving hardness.
    [Show full text]
  • Exactly Solving Packing Problems with Fragmentation
    Exactly solving packing problems with fragmentation M. Casazza, A. Ceselli, Università degli Studi di Milano, Dipartimento di Informatica, OptLab – Via Bramante 65, 26013 – Crema (CR) – Italy {marco.casazza, alberto.ceselli}@unimi.it April 13, 2015 In packing problems with fragmentation a set of items of known weight is given, together with a set of bins of limited capacity; the task is to find an assignment of items to bins such that the sum of items assigned to the same bin does not exceed its capacity. As a distinctive feature, items can be split at a price, and fractionally assigned to different bins. Arising in diverse application fields, packing with fragmentation has been investigated in the literature from both theoretical, modeling, approximation and exact optimization points of view. We improve the theoretical understanding of the problem, and we introduce new models by exploiting only its combinatorial nature. We design new exact solution algorithms and heuristics based on these models. We consider also variants from the literature arising while including different objective functions and the option of handling weight overhead after splitting. We present experimental results on both datasets from the literature and new, more challenging, ones. These show that our algorithms are both flexible and effective, outperforming by orders of magnitude previous approaches from the literature for all the variants considered. By using our algorithms we could also assess the impact of explicitly handling split overhead, in terms of both solutions quality and computing effort. Keywords: Bin Packing, Item Fragmentation, Mathematical Programming, Branch&Price 1 1 Introduction Logistics has always been a benchmark for combinatorial optimization methodologies, as practitioners are traditionally familiar with the competitive advantage granted by optimized systems.
    [Show full text]
  • Solving Packing Problems with Few Small Items Using Rainbow Matchings
    Solving Packing Problems with Few Small Items Using Rainbow Matchings Max Bannach Institute for Theoretical Computer Science, Universität zu Lübeck, Lübeck, Germany [email protected] Sebastian Berndt Institute for IT Security, Universität zu Lübeck, Lübeck, Germany [email protected] Marten Maack Department of Computer Science, Universität Kiel, Kiel, Germany [email protected] Matthias Mnich Institut für Algorithmen und Komplexität, TU Hamburg, Hamburg, Germany [email protected] Alexandra Lassota Department of Computer Science, Universität Kiel, Kiel, Germany [email protected] Malin Rau Univ. Grenoble Alpes, CNRS, Inria, Grenoble INP, LIG, 38000 Grenoble, France [email protected] Malte Skambath Department of Computer Science, Universität Kiel, Kiel, Germany [email protected] Abstract An important area of combinatorial optimization is the study of packing and covering problems, such as Bin Packing, Multiple Knapsack, and Bin Covering. Those problems have been studied extensively from the viewpoint of approximation algorithms, but their parameterized complexity has only been investigated barely. For problem instances containing no “small” items, classical matching algorithms yield optimal solutions in polynomial time. In this paper we approach them by their distance from triviality, measuring the problem complexity by the number k of small items. Our main results are fixed-parameter algorithms for vector versions of Bin Packing, Multiple Knapsack, and Bin Covering parameterized by k. The algorithms are randomized with one-sided error and run in time 4k · k! · nO(1). To achieve this, we introduce a colored matching problem to which we reduce all these packing problems. The colored matching problem is natural in itself and we expect it to be useful for other applications.
    [Show full text]
  • A Width Parameter Useful for Chordal and Co-Comparability Graphs
    A width parameter useful for chordal and co-comparability graphs Dong Yeap Kang1, O-joung Kwon2, Torstein J. F. Strømme3, and Jan Arne Telle3 ? 1 Department of Mathematical Sciences, KAIST, Daejeon, South Korea 2 Institute of Software Technology and Theoretical Computer Science, TU Berlin, Germany 3 Department of Informatics, University of Bergen, Norway [email protected], [email protected], [email protected], [email protected] Abstract. In 2013 Belmonte and Vatshelle used mim-width, a graph parameter bounded on interval graphs and permutation graphs that strictly generalizes clique-width, to explain existing algorithms for many domination-type problems, also known as (σ; ρ)- problems or LC-VSVP problems, on many special graph classes. In this paper, we focus on chordal graphs and co-comparability graphs, that strictly contain interval graphs and permutation graphs respectively. First, we show that mim-width is unbounded on these classes, thereby settling an open problem from 2012. Then, we introduce two graphs Kt Kt and Kt St to restrict these graph classes, obtained from the disjoint union of two cliques of size t, and one clique of size t and one independent set of size t respec- tively, by adding a perfect matching. We prove that (Kt St)-free chordal graphs have mim-width at most t − 1, and (Kt Kt)-free co-comparability graphs have mim-width at most t − 1. From this, we obtain several algorithmic consequences, for instance, while Dominating Set is NP-complete on chordal graphs, like all LC-VSVP problems it can be solved in time O(nt) on chordal graphs where t is the maximum among induced sub- graphs Kt St in the given graph.
    [Show full text]
  • Jigsaw Puzzles, Edge Matching, and Polyomino Packing: Connections and Complexity∗
    Jigsaw Puzzles, Edge Matching, and Polyomino Packing: Connections and Complexity∗ Erik D. Demaine, Martin L. Demaine MIT Computer Science and Artificial Intelligence Laboratory, 32 Vassar St., Cambridge, MA 02139, USA, {edemaine,mdemaine}@mit.edu Dedicated to Jin Akiyama in honor of his 60th birthday. Abstract. We show that jigsaw puzzles, edge-matching puzzles, and polyomino packing puzzles are all NP-complete. Furthermore, we show direct equivalences between these three types of puzzles: any puzzle of one type can be converted into an equivalent puzzle of any other type. 1. Introduction Jigsaw puzzles [37,38] are perhaps the most popular form of puzzle. The original jigsaw puzzles of the 1760s were cut from wood sheets using a hand woodworking tool called a jig saw, which is where the puzzles get their name. The images on the puzzles were European maps, and the jigsaw puzzles were used as educational toys, an idea still used in some schools today. Handmade wooden jigsaw puzzles for adults took off around 1900. Today, jigsaw puzzles are usually cut from cardboard with a die, a technology that became practical in the 1930s. Nonetheless, true addicts can still find craftsmen who hand-make wooden jigsaw puzzles. Most jigsaw puzzles have a guiding image and each side of a piece has only one “mate”, although a few harder variations have blank pieces and/or pieces with ambiguous mates. Edge-matching puzzles [21] are another popular puzzle with a similar spirit to jigsaw puzzles, first appearing in the 1890s. In an edge-matching puzzle, the goal is to arrange a given collection of several identically shaped but differently patterned tiles (typically squares) so that the patterns match up along the edges of adjacent tiles.
    [Show full text]
  • Graceful Labeling of Graphs
    GRACEFUL LABELING OF GRAPHS Rodrigo Ming Zhou Dissertação de Mestrado apresentada ao Programa de Pós-graduação em Engenharia de Sistemas e Computação, COPPE, da Universidade Federal do Rio de Janeiro, como parte dos requisitos necessários à obtenção do título de Mestre em Engenharia de Sistemas e Computação. Orientadores: Celina Miraglia Herrera de Figueiredo Vinícius Gusmão Pereira de Sá Rio de Janeiro Dezembro de 2016 GRACEFUL LABELING OF GRAPHS Rodrigo Ming Zhou DISSERTAÇÃO SUBMETIDA AO CORPO DOCENTE DO INSTITUTO ALBERTO LUIZ COIMBRA DE PÓS-GRADUAÇÃO E PESQUISA DE ENGENHARIA (COPPE) DA UNIVERSIDADE FEDERAL DO RIO DE JANEIRO COMO PARTE DOS REQUISITOS NECESSÁRIOS PARA A OBTENÇÃO DO GRAU DE MESTRE EM CIÊNCIAS EM ENGENHARIA DE SISTEMAS E COMPUTAÇÃO. Examinada por: Prof. Celina Miraglia Herrera de Figueiredo, D.Sc. Prof. Vinícius Gusmão Pereira de Sá, D.Sc. Prof. Rosiane de Freitas Rodrigues, D.Sc. Prof. Raphael Carlos Santos Machado, D.Sc. RIO DE JANEIRO, RJ – BRASIL DEZEMBRO DE 2016 Zhou, Rodrigo Ming Graceful Labeling of Graphs/Rodrigo Ming Zhou. – Rio de Janeiro: UFRJ/COPPE, 2016. IX, 40 p.: il.; 29; 7cm. Orientadores: Celina Miraglia Herrera de Figueiredo Vinícius Gusmão Pereira de Sá Dissertação (mestrado) – UFRJ/COPPE/Programa de Engenharia de Sistemas e Computação, 2016. Bibliography: p. 38 – 40. 1. graceful labeling. 2. computational proofs. 3. graphs. I. de Figueiredo, Celina Miraglia Herrera et al. II. Universidade Federal do Rio de Janeiro, COPPE, Programa de Engenharia de Sistemas e Computação. III. Título. iii Resumo da Dissertação apresentada à COPPE/UFRJ como parte dos requisitos necessários para a obtenção do grau de Mestre em Ciências (M.Sc.) GRACEFUL LABELING OF GRAPHS Rodrigo Ming Zhou Dezembro/2016 Orientadores: Celina Miraglia Herrera de Figueiredo Vinícius Gusmão Pereira de Sá Programa: Engenharia de Sistemas e Computação Em 1966, A.
    [Show full text]
  • Improved Lower Bounds for Graph Embedding Problems
    Improved Lower Bounds for Graph Embedding Problems Hans L. Bodlaender1;2? and Tom C. van der Zanden1 1 Department of Computer Science, Utrecht University, Utrecht, The Netherlands fH.L.Bodlaender,[email protected] 2 Department of Mathematics and Computer Science, Eindhoven University of Technology, Eindhoven, The Netherlands Abstract. In this paper, we give new, tight subexponential lower bounds for a number of graph embedding problems. We introduce two related combinatorial problems, which we call String Crafting and Orthog- onal Vector Crafting, and show that these cannot be solved in time 2o(jsj= log jsj), unless the Exponential Time Hypothesis fails. These results are used to obtain simplified hardness results for several graph embedding problems, on more restricted graph classes than previ- ously known: assuming the Exponential Time Hypothesis, there do not exist algorithms that run in 2o(n= log n) time for Subgraph Isomorphism on graphs of pathwidth 1, Induced Subgraph Isomorphism on graphs of pathwidth 1, Graph Minor on graphs of pathwidth 1, Induced Graph Minor on graphs of pathwidth 1, Intervalizing 5-Colored Graphs on trees, and finding a tree or path decomposition with width at most c with a minimum number of bags, for any fixed c ≥ 16. 2Θ(n= log n) appears to be the \correct" running time for many pack- ing and embedding problems on restricted graph classes, and we think String Crafting and Orthogonal Vector Crafting form a useful framework for establishing lower bounds of this form. 1 Introduction Many NP-complete graph problems admit faster algorithms when restricted to planar graphs.
    [Show full text]