Locating regions in a sequence under density constraints

Several biological problems require the identification of regions in a sequence where some feature occurs within a target density range: examples including the location of GC-rich regions, identification of CpG islands, and sequence matching. Mathematically, this corresponds to searching a string of 0s and 1s for a substring whose relative proportion of 1s lies between given lower and upper bounds. We consider the algorithmic problem of locating the longest such substring, as well as other related problems (such as finding the shortest substring or a maximal set of disjoint substrings). For locating the longest such substring, we develop an algorithm that runs in O(n) time, improving upon the previous best-known O(n log n) result. For the related problems we develop O(n log log n) algorithms, again improving upon the best-known O(n log n) results. Practical testing verifies that our new algorithms enjoy significantly smaller time and memory footprints, and can process sequences that are orders of magnitude longer as a result.Comment: 17 pages, 8 figures; v2: minor revisions, additional explanations; to appear in SIAM Journal on Computin

Creating informatics olympiad tasks: Exploring the black art

Each year a wealth of informatics olympiads are held worldwide at national, regional and international levels, all of which require engaging and challenging tasks that have not been seen before. Nevertheless, creating high quality tasks can be a difficult and time-consuming process. In this paper we explore some of the different techniques that problem setters can use to find new ideas for tasks and refine these ideas into problems suitable for an informatics olympiad. These techniques are illustrated through concrete examples from a variety of contests

Coding Tutorials for any Programming Language or Interactive Tutorials for C and Arduino

International audienc

Get involved! The IOI workshop 2010, its goals and results

In May 2010, the third IOI workshop took place in Schloss Dagstuhl, Germany. It was motivated by the discussions held at and after the panel session of 2009's IOI conference in Plovdiv. There, discussions focussed on communication and collaboration among the IOI community, as well as communication of the IOI competition to outsiders. At the workshop, members of the IOI community met to develop a first version of an IOI Wiki as a tool for communication and collaboration, and devised suggestions on how to visualize IOI-style contests to make them more accessible to the outside world