Using modular arithmetic as a case study, this research aims to explore, with an interdisciplinary view between Mathematics and Informatics, the ways in which students use algorithms, strategies and heuristics in problem solving activities. In particular, an analytical tool has been developed to analyse the different approaches used by students when confronted with a task at the boundary between Mathematics and Informatics. Our work has provided insights on how such a tool allows a possible characterisation of different problem solving approaches, which may be more oriented towards Mathematics or closer to Informatics, and could be a useful tool in the analysis of tasks to be proposed to students, in order to highlight the characteristics considered useful for the development of algorithmic thinking.