We study dynamic membership problems for the Dyck languages, the class of strings of properly balanced parentheses. We also study the Dynamic Word problem for the free group. We present deterministic algorithms and data structures which maintain a string under replacements of symbols, insertions, and deletions of symbols, and language membership queries. Updates and queries are handled in polylogarithmic time. We also give both Las Vegas- and Monte Carlo-type randomised algorithms to achieve better running times, and present lower bounds on the complexity for variants of the problems.

Unauthorized re-use of code by students is a widespread problem in academic institutions, and raises liability issues for industry. Manual plagiarism detection is time-consuming, and current effective plagiarism detection approaches cannot be easily scaled to very large code repositories. While there are practical text-based plagiarism detection systems capable of working with large collections, this is not the case for code-based plagiarism detection. In this paper, we propose techniques for detecting plagiarism in program code using text similarity measures and local alignment. Through detailed empirical evaluation on small and large collections of programs, we show that our approach is highly scalable while maintaining similar levels of effectiveness to that of the popular JPlag and MOSS systems. Copyright c ○ 2006 John Wiley

The copying of programming assignments is a widespread problem in academic institutions. Manual plagiarism detection is time-consuming, and current popular plagiarism detection systems are not scalable to large code repositories. While there are text-based plagiarism detection systems capable of handling millions of student papers, comparable systems for code-based plagiarism detection are in their infancy. In this thesis, we propose and evaluate new techniques for code plagiarism detection. Using small and large collections of programs, we show that our approach is highly scalable while maintaining similar levels of effectiveness to that of JPlag. 1 Declaration I declare that this work is entirely my own except where due acknowledgement has been made and