Contests and Olympiads should be considered not only as a way of comparing the students' levels of training. They can be regarded as a different way of organizing the mental activity of participants. Different types of tasks initiate various types of intellectual activity among students. The Olympiad tasks differ from "school" ones by non-standardness, a combination of the understandability of the formulation and the non-obviousness of the solution, the possibility of various approaches to solving the problem. At the same time, the variety of contests and Olympiads raises the task of investigating and classifying them, focusing on supporting different styles of thinking. In this paper, we carry out an analysis of contests and Olympiads in informatics, aiming at identifying aspects of the student's intellectual activity, which are not sufficiently evaluated at school. The Olympiad in Discrete Mathematics and Theorethical Informatics is at the intersection of the two sciences. The article deals with the problems encountered by the organizers of competitions in mathematics and computer science and demonstrates some ways to solve them using the example of the Olympiad.