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Olympiads Olympiads inin Informatics Informatics Olympiads VolumeVolume 7, 2013 7 2013 S. COMBÉFIS, V. VAN den SCHRIECK, A. NOOTENS. Growing Algorithmic in Informatics Thinking Through Interactive Problems to Encourage Learning Programming 3 M. DOLINSKY. An Approach to Teaching Introductory-Level Computer Programming 14 Olympiads in Informatics 7 M. FORIŠEK. Pushing the Boundary of Programming Contests 23 S. HALIM. Expecting the Unexpected 36 M. JOVANOV, B. KOSTADINOV, E. STANKOV, M. MIHOVA, M. GUSEV. State Competitions in Informatics and the Supporting Online Learning and Contest Management System with Collaboration and Personalization Features MENDO 42 M. MAREŠ. Computer Maintenance via Batch Execution 55 M. MARKOV, K. MANEV. Algorithmic Results on a Novel Computational Problem 61 M. OPMANIS. Latvian Olympiad in Informatics – Lessons Learned 78 J. PACHOCKI, J. RADOSZEWSKI. Where to Use and How not to Use Polynomial String Hashing 90 P.S. PANKOV. Tasks in Informatics of Continuous Content 101 SIMON. Olympiads in Informatics – the Journal’s First Six Years 113 E. STANKOV, M. JOVANOV, A. BOJCHEVSKI, A. MADEVSKA BOGDANOVA. EMAx: Software for C++ Source Code Analysis 123 Volume 7, 2013 Volume W. van der VEGT. Predicting the Difficulty Level of a Bebras Task 132 T. VERHOEFF. Informatics Everywhere: Information and Computation in Society, Science, and Technology 140 REPORTS A. IGLIKOV, Z. GAMEZARDASHVILI, B. MATKARIMOV. International Olympiads in Informatics in Kazakhstan 153 M. KAYKOBAD. Bangladesh Olympiads in Informatics 163 G. MANDARIA. Olympiads in Informatics: the Georgian Experience 168 M. MUKUND. The Indian Computing Olympiad 175 Q. ZHAO, F. WANG, B. YIN, H. SUN. Arbiter: the Evaluation Tool in the Contests of the China NOI 180 REVIEWS, COMMENTS 186 Ics IOI In Informat Iad olymp Ional ISSN 1822-7732 Internat ISSN 1822-7732 INTERNATIONAL OLYMPIAD IN INFORMATICS VILNIUS UNIVERSITY INSTITUTE OF MATHEMATICS AND INFORMATICS OLYMPIADS IN INFORMATICS Volume 7 2013 Selected papers of the International Conference joint with the XXV International Olympiad in Informatics Brisbane, Australia, July 6–13, 2013 OLYMPIADS IN INFORMATICS ISSN 1822-7732 Editor-in-Chief Valentina Dagiene˙ 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] Marcin Kubica, Warsaw University, Poland, [email protected] Ville Leppänen, University of Turku, Finland, [email protected].fi Krassimir Manev, Sofia University, Bulgaria, [email protected]fia.bg Rein Prank, University of Tartu, Estonia, [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] http://www.mii.lt/olympiads_in_informatics Publisher: Vilnius University Institute of Mathematics and Informatics c Vilnius University, 2013 Akademijos 4, LT-08663 Vilnius, Lithuania All rights reseserved Olympiads in Informatics, 2013, Vol. 7, 1–2 1 © 2013 Vilnius University Foreword It passed unremarked in the introduction to the 6th volume of Olympiads in Infor- matics but that volume brought the number of full articles published by the conference to 101. For an event held in partnership with the International Olympiad in Informatics, or the IOI as it is frequently called, a rather satisfactory co-incidence. So why was it not mentioned until highlighted in this volume’s paper on the journal’s first few years? The number might, perhaps, have been left unmentioned because it is just a bit of fun. The type of numerology that might appear semi-seriously in the popular press, less- seriously mentioned in a volume of recreational mathematics; merely a co-incidence and one that, after all, requires the exclusion of some of the journal’s contents (such as re- views). Making this deduction however ignores the fact that, for many of those who participate in both the conference and the olympiad, a lot of this is fun. These 101 papers all have serious content – and a huge amount of work goes in to running national and international olympiads – but there is pleasure in running these events, seeing students flourish and seeing colleagues. Even students have been known to have a good time. It is certainly not because, as a community, we have no interest in numbers. Many of the papers that we have published derive some basic spark, some essential essence, from figures. We have looked at, and continue to look at, how we can go about measuring tasks; how should we grade and assign marks, in what ways is it meaningful to time evaluation, etc...Severalpapers have categorised and by extension counted tasks in those categories, before looking at student performance. If we removed combinatorics from the problems we set we would run very different types of contests. Our community’s interest in numbers goes beyond the technical aspects. We care about the number of students we bring in to our national events and we want to see that different groups are represented. The varied country reports that have been published since 2007 show the varied ways in which our national contests are run. We can use this knowledge to pick from success stories around the world and if, perhaps, a comparison with the numbers from elsewhere is occasionally humbling, it can drive us forward. The real reason, of course, why the 101–IOI synchronicity was not considered in the 6th volume’s editorial was that it was unknown to the editors. It took the observation from someone outside our usual community to mention the number. It has been an aim of the conference, since it was established, to become part of, and bring in, the wider pedagogical community. We have not had many papers authored from those outside the IOI but they are starting to appear. In this volume we report on two PhD thesis published in related areas. The fact that such research is taking place, both within these pages and outside, is delightful. Long may it continue. 2 As always thanks are due to all those who have assisted with the current volume – au- thors, 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. Peer re- viewing all of the papers takes a significant amount of time and work and special thanks should be given to those otherwise unsung reviewing heroes: Jonas Blonskis, Andrej Brodnik, Hugo Duenas, Michael Forišek, Gerald Futschek, Mathias Hiron, Rob Kolstad, Ville Leppänen, Krassimir Manev, Marti¸¯ nš Opmanis, Rhein Prank, Miguel Revilla, Jurat¯ e˙ Skupien¯ e,˙ Ahto Truu, Tom Verhoeff. Last, but by no means least, particular thanks are due to the organisational commit- tee for IOI’2013 in Australia without whose assistance we would be unable to hold the conference. Their assistance, during what is an already busy period, is gratefully received. Editors Olympiads in Informatics, 2013, Vol. 7, 3–13 3 © 2013 Vilnius University Growing Algorithmic Thinking Through Interactive Problems to Encourage Learning Programming Sébastien COMBÉFIS1,3, Virginie VAN den SCHRIECK2, Alexis NOOTENS3 1Department of Computer Science Engineering, Université catholique de Louvain Place Sainte Barbe 2, 1348 Louvain-la-Neuve, Belgium 2École Pratique des Hautes Études Commerciales (EPHEC) Avenue du Ciseau 15, 1348 Louvain-la-Neuve, Belgium 3Computer Science and IT in Education ASBL, Belgium e-mail: sebastien.combefi[email protected], [email protected], [email protected] Abstract. Attracting pupils from secondary schools (12–18 years old) to learn programming is not easy. It is especially the case in Belgium where there is no or very few programming and algorithm design courses in secondary schools. Another issue is that teachers who are in charge of computer science courses are afraid of teaching a matter they do not feel comfortable with, especially when they are not informatics teachers. This paper presents ILPADS, interactive learning of program- ming and algorithm design skills, an interactive website which aims at gradually growing algorith- mic thinking skills to lead pupils towards the learning of the Python programming language. That website aims to serve as working material to support teachers for their computer science courses in secondary schools. Pupils can also use the website at home to continue learning on their own. The paper presents the interactive website and mainly focuses on the design of the ILPADS activities. Future work includes testing the website in real classrooms and evaluating it. Key words: algorithmic thinking, learning programming, teaching, distance learning, interactive learning. 1. Introduction Trying to attract more pupils to participate at the International Olympiad in Informatics (IOI) is not an easy task. It is especially the case in countries like Belgium where there are no or only a few computer science related courses in secondary schools (12–18 years old). Although there are pupils that are good at programming and designing algorithms, some of them may just ignore it and they consequently will not participate to the selection for the IOI (Combéfis and Leroy, 2011). Moreover, there are no or few computer science teachers in the secondary schools of those countries where informatics is not part of the curriculum. That latter fact does not ease the task of introducing computer science and especially programming to the pupils. In such countries, it is even more difficult to develop and propose activities to be organised by the teachers in their classrooms, since they do not feel comfortable with the material to teach. 4 S. Combéfis et al. One possible way to propose activities to pupils is through online platforms. Vari- ous platforms, such as Pythia (Combéfis and Le Clément de Saint-Marcq, 2012), Putka (Urbanciˇ cˇ and Trampuš, 2012) or France-IOI (Hiron and Février, 2012) do exist but are mainly focused on directly teaching programming.