Keeping count of variable occurence in google OR Tools

Question

I'm playing around with OR Tools, just wondering if there is any way to hold the number of times a certain constraint is satisfied?

In this case, I'd like to keep track of the number of times my 'diff' variable is -1, -2, 0, 2 , etc.

I've gotten the solution printer from the official documentation, so would I have to edit/tweak that in any way to return count as well?

Thanks in advance, I'm new to this.

from ortools.sat.python import cp_model
model = cp_model.CpModel()
x = model.NewIntVar(0, 10, 'x')
y = model.NewIntVar(0, 10, 'y')
diff = model.NewIntVar(-10,10,'diff')
model.Add(diff == x - y)
#occurences of each diff

#solution printer
class VarArraySolutionPrinter(cp_model.CpSolverSolutionCallback):
    """Print intermediate solutions."""

    def __init__(self, variables):
        cp_model.CpSolverSolutionCallback.__init__(self)
        self.__variables = variables
        self.__solution_count = 0

    def on_solution_callback(self):
        self.__solution_count += 1
        for v in self.__variables:
            print(f"{v}={self.Value(v)}", end=" ")
        print()

    def solution_count(self):
        return self.__solution_count

solver = cp_model.CpSolver()
# solver.parameters.log_search_progress = True
solution_printer = VarArraySolutionPrinter([x, y, diff])
solver.parameters.enumerate_all_solutions = True
status = solver.Solve(model, solution_printer)

Answer 1

Why don't you just increase a counter in the on_solution_callback() method ?