A Weighted Constraint Optimization Approach to the Nurse Scheduling Problem

As a solution proposal for the Second International Nurse Rostering Competition (INRC-II) [1], we introduce in this paper an approach based on the weighted constraint satisfaction problem (WCSP). The WCSP, given a number of constraints (both hard constraints - ones that must not be violated, and soft constraints - ones that influence the degree of optimality of a possible solution) aims to minimize the total weight of all unsatisfied constraints. We propose an heuristic based approach to the WCSP, using a general constraint satisfaction solver whose configuration was specifically adapted to the nurse scheduling problem presented by the INRC-II competition. Several problems were solved using our approach in order to better tweak the heuristic settings, the results of which are presented in this document, as well as the best implementation of the solver found so far.