stop_after_n_solutions_sample_sat.py

# Copyright 2010-2018 Google LLC
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Code sample that solves a model and displays a small number of solutions."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from ortools.sat.python import cp_model


class VarArraySolutionPrinterWithLimit(cp_model.CpSolverSolutionCallback):
    """Print intermediate solutions."""

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

    def on_solution_callback(self):
        self.__solution_count += 1
        for v in self.__variables:
            print('%s=%i' % (v, self.Value(v)), end=' ')
        print()
        if self.__solution_count >= self.__solution_limit:
            print('Stop search after %i solutions' % self.__solution_limit)
            self.StopSearch()

    def solution_count(self):
        return self.__solution_count


def StopAfterNSolutionsSampleSat():
    """Showcases calling the solver to search for small number of solutions."""
    # Creates the model.
    model = cp_model.CpModel()
    # Creates the variables.
    num_vals = 3
    x = model.NewIntVar(0, num_vals - 1, 'x')
    y = model.NewIntVar(0, num_vals - 1, 'y')
    z = model.NewIntVar(0, num_vals - 1, 'z')

    # Create a solver and solve.
    solver = cp_model.CpSolver()
    solution_printer = VarArraySolutionPrinterWithLimit([x, y, z], 5)
    status = solver.SearchForAllSolutions(model, solution_printer)
    print('Status = %s' % solver.StatusName(status))
    print('Number of solutions found: %i' % solution_printer.solution_count())
    assert solution_printer.solution_count() == 5


StopAfterNSolutionsSampleSat()