# Copyright 2010 Hakan Kjellerstrand hakank@bonetmail.com
#
# 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.

"""

  Set covering in Google CP Solver.

  Example 9.1-2, page 354ff, from
  Taha 'Operations Research - An Introduction'
  Minimize the number of security telephones in street
  corners on a campus.

  Compare with the following models:
  * MiniZinc: http://www.hakank.org/minizinc/set_covering2.mzn
  * Comet   : http://www.hakank.org/comet/set_covering2.co
  * ECLiPSe : http://www.hakank.org/eclipse/set_covering2.ecl
  * SICStus: http://hakank.org/sicstus/set_covering2.pl
  * Gecode: http://hakank.org/gecode/set_covering2.cpp

  This model was created by Hakan Kjellerstrand (hakank@bonetmail.com)
  Also see my other Google CP Solver models: http://www.hakank.org/google_or_tools/

"""

from constraint_solver import pywrapcp

def main(unused_argv):

    # Create the solver.
    solver = pywrapcp.Solver('Set covering')

    #
    # data
    #
    n = 8 # maximum number of corners
    num_streets = 11 # number of connected streets


    # corners of each street
    # Note: 1-based (handled below)
    corner = [
        [1,2],
        [2,3],
        [4,5],
        [7,8],
        [6,7],
        [2,6],
        [1,6],
        [4,7],
        [2,4],
        [5,8],
        [3,5]
        ]

    #
    # declare variables
    #
    x = [solver.IntVar(0, 1, 'x[%i]' % i) for i in range(n)]

    #
    # constraints
    #

    # number of telephones, to be minimized
    z = solver.Sum(x)

    # ensure that all corners are covered
    for i in range(num_streets):
        # also, convert to 0-based
        solver.Add(solver.SumGreaterOrEqual([x[j - 1] for j in corner[i]], 1))

    objective = solver.Minimize(z, 1)

    #
    # solution and search
    #
    solution = solver.Assignment()
    solution.Add(x)
    solution.AddObjective(z)

    collector = solver.LastSolutionCollector(solution)
    solver.Solve(solver.Phase(x,
                              solver.INT_VAR_DEFAULT,
                              solver.INT_VALUE_DEFAULT),
                 [collector, objective])

    print "z:", collector.ObjectiveValue(0)
    print "x:", [collector.Value(0, x[i]) for i in range(n)]

    print "failures:", solver.Failures()
    print "branches:", solver.Branches()
    print "WallTime:", solver.WallTime()


if __name__ == '__main__':
    main("cp sample")