ISSN 1822-7732 INTERNATIONAL OLYMPIAD IN INFORMATICS VILNIUS UNIVERSITY INSTITUTE OF MATHEMATICS AND INFORMATICS OLYMPIADS IN INFORMATICS Volume 8 2014 Selected papers of the International Conference joint with the XXVI International Olympiad in Informatics Taipei, Taiwan, July 13-20, 2014 OLYMPIADS IN INFORMATICS Editor-in-Chief Valentina Dagienė Vilnius University, Lithuania, [email protected] Executive Editor Richard Forster British Informatics Olympiad, UK, [email protected] International Editorial Board Gerald Futschek, Vienna University of Technology, Austria, [email protected] Bruria Haberman, Holon Institute of Technology, Israel, [email protected] Mile Jovanov, Sts. Cyril and Methodius University, Skopje, Macedonia, [email protected] Marcin Kubica, Warsaw University, Poland, [email protected] Ville Leppänen, University of Turku, Finland, [email protected] Krassimir Manev, Sofia University, Bulgaria, [email protected] Rein Prank, University of Tartu, Estonia, [email protected] Seiichi Tani, Nihon University, Japan, [email protected] Peter Taylor, University of Canberra, Australia, [email protected] Troy Vasiga, University of Waterloo, Canada, [email protected] Peter Waker, International Qualification Alliance, Republic of South Africa, [email protected] Willem van der Vegt, Windesheim University for Applied Sciences, The Netherlands, [email protected] http://ioinformatics.org/oi_index.shtml http://www.mii.lt/olympiads_in_informatics ISSN 1822-7732 (Print) 2335-8955 (Online) Publisher: Vilnius University © Vilnius University, 2014 Institute of Mathematics and Informatics International Olympiad in Informatics, 2 0 1 4 Akademijos str. 4, LT-08663 Vilnius, Lithuania All rights reserved Olympiads in Informatics, 2014, Vol. 8, 1–2 1 © 2014 Vilnius University, IOI Foreword In the first years of the Olympiads in Informatics conference a specific theme was set. Since 2009 papers have been accepted on any topic that falls under our remit – along with the occasional one that falls just outside. One way of splitting these papers is into those that relate to olympiads and those that look at the wider teaching of informat- ics. Many of the conference’s earlier papers, when not discussing contest technicalities (tasks, graders, etc…) looked towards the organisational aspects of the events. We are now seeing papers that take as their foundation national strategies for teaching, of which an informatics olympiad is (if at all) a small part. We are fortunate to deal with a subject that adapts well to new technology. As an illustration consider the International Olympiad in Informatics which has moved from manual grading to automated grading; originally requiring evaluators typing in data by hand, moving to evaluators running semi-automated systems, to our current state of au- tomated grading which can – on a good day – have the results of the event ready before the students have left the contest area. What is more exciting is to see these same grad- ing systems being adapted outside of the contest environment and becoming part of the pedagogical one. We live in a world containing teachers with a mix of abilities, knowledge and moti- vations. Schools where there are limits on the amount of time to teach and the resources to teach with. Students who need to work hard on the simplest materials; those who are able to rush ahead to the complex; those who want to study the esoteric. The last few years, especially through the internet, have seen an explosion of courses that are avail- able outside of the usual teaching environment. Again – we are fortunate to deal with a subject that adapts well to new technology. One where automated systems can give accurate feedback to students. One where, without specialist equipment, students can study at their own rate. The development of grading and teaching environments within our community, and their spread to the wider teaching community, is one of our strengths. There is now a real choice of several strong environments that we have created and made available. This volume contains several papers discussing such systems; their technical aspects but also how they can be used to teach. It is not just our top students who are benefiting from the olympiads; not just those who compete in our contests. We are making a real difference out there. As always thanks are due to all those who have assisted with the current volume – authors, reviewers and editors. A lot of work goes, not only to the writing of the papers, but to an extended period of review and correction and, in several cases, translation. 2 Peer reviewing all of the papers takes a significant amount of time and work and special thanks should be given to those otherwise unsung reviewing heroes. Last, but by no means least, particular thanks are due to the organisational committee for IOI’2014 in Taiwan without whose assistance we would be unable to hold the confer- ence. Their assistance, during what is an already busy period, is gratefully received. Editors Olympiads in Informatics, 2014, Vol. 8, 3–19 3 © 2014 Vilnius University, IOI Presenting Computer Science Concepts to High School Students Tim BELL1, Caitlin DUNCAN1, Sam JARMAN1, Heidi NEWTON2 1 University of Canterbury, New Zealand 2 Victoria University of Wellington, New Zealand e-mail: [email protected], [email protected], [email protected], [email protected] Abstract. Computer science at high school often focuses on programming, but a broader view of other areas of computer science has key benefits for both writing programs that are more efficient and making more theoretical concepts more accessible to those who do not find programming in- trinsically interesting. With the introduction of computer science at high schools, a lack of coherent resources for teachers and students prompted the development of the NZ Computer Science Field Guide, an open-source, on-line textbook. This paper describes the design of the Field Guide, which has fourteen chapters about various topics of computer science. The design includes written text, videos, classroom activities and inter- active applications. The need for a broad view of computer science is discussed, and programming exercises to go with the topics are suggested. Keywords: computer science, high school, curriculum, constructivism, open source. 1. Introduction Computer science at high school level often focuses on programming, but new ap- proaches, including new curricula in the UK (Furber, 2012), Australia (Falkner et al., 2014) and New Zealand (Bell et al., 2010), are being developed that offer a broader view of the subject, allowing students to delve into topics such as algorithm efficiency, encryption, human computer interaction and computer vision. This broader view has two key benefits: first, it shows programmers how to write programs that are more effective, and second, for those who don’t find programming intrinsically interesting, it shows the kinds of things that are done with programming, providing the motivation to learn programming. For example, in programming competitions students are tasked with problems to solve that must run within a time limit. Writing a program to solve a problem may not be so difficult, but to do it efficiently and effectively can involve bringing to bear ideas from computer science (such as algorithmic complexity and tractability), and a good un- derstanding of computer science principles can enable students to improve their compe- tition code, allowing it to execute faster and fit under time limits set by the judges. Con- versely, ideas from computer science (such as data compression or formal languages) 4 T. Bell et al. can provide rich domains for programming exercises, and give students more experience thinking about the richness of approaches available to the computer scientist, such as hashing (an idea which can be applied to areas as diverse as searching algorithms, error detection by hash totals, and password encryption by secure hashing). Although there are literally thousands of resources available that touch on areas of computer science that might be relevant to high school level students (Murugesh et al., 2010), these resources vary greatly in suitability, and tend to occur as one-off examples that can’t be used as a coherent body. To address this, we have developed the “NZ Com- puter Science Field Guide” (referred to here as the NZ CSFG, available at http:// csfieldguide.org.nz), an open-source, interactive, online “textbook” that intro- duces a wide range of topics in computer science, without necessarily expecting students to be competent programmers before tackling the range of topics covered. It is a pilot for a wider range of computer science field guides intended for international use in a variety of contexts. The index of the NZ CSFG is shown in Fig. 1, showing the range of topics covered. The NZ CSFG has initially been developed to support the new computer science stan- dards that became available in New Zealand high schools in 2011 (Bell et al., 2010), but it is intended to be flexible enough to support curricula for other countries, and other initiatives aimed at high school aged students, such as computing clubs and programming competitions. Because it is open source, in principle educators can adapt it to suit their situation. Because it is online it can be accessed by interested students as long as they have internet access, and an offline version is planned so that it can be delivered through other media as well. For example, while the NZ CSFG was initially prepared to support teaching computer science in New Zealand high schools, it was also being used in parallel to sup- port a pilot for a Computer Science Club (http://computerscienceclub.org) for students aged around 10 to 15 years old. The club is based on a badge system where students can attain different levels of badges in topics in computer science, with many of the badge topics being associated with topics in the CSFG.