ISSN 1822-7732 INTERNATIONAL OLYMPIAD IN INFORMATICS VILNIUS UNIVERSITY OLYMPIADS IN INFORMATICS Volume 13 2019 Selected papers of the International Conference joint with the XXXI International Olympiad in Informatics Baku, Azerbaijan, 4–11 August, 2019 OLYMPIADS IN INFORMATICS Editor-in-Chief Valentina Dagienė Vilnius University, Lithuania,
[email protected] Executive Editor Mile Jovanov, Sts. Cyril and Methodius University, Macedonia,
[email protected] Technical Editor Tatjana Golubovskaja Vilnius University, Lithuania,
[email protected] International Editorial Board Benjamin Burton, University of Queensland, Australia,
[email protected] Sébastien Combéfis, Computer Science and IT in Education NPO, Belgium,
[email protected] Michal Forišek, Comenius University, Bratislava, Slovakia,
[email protected] Gerald Futschek, Vienna University of Technology, Austria,
[email protected] Marcin Kubica, Warsaw University, Poland,
[email protected] Ville Leppänen, University of Turku, Finland,
[email protected] Krassimir Manev, New Bulgarian University, Bulgaria,
[email protected] Seiichi Tani, Nihon University, Japan,
[email protected] Peter Waker, International Qualification Alliance, South Africa,
[email protected] Willem van der Vegt, Windesheim University for Applied Sciences, The Netherlands,
[email protected] The journal Olympiads in Informatics is an international open access journal devoted to publishing original research of the highest quality in all aspects of learning