# 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.
"""
Map coloring problem in Google CP Solver.
From Pascal Van Hentenryck 'The OPL Optimization Programming Language',
page 7, 42.
Compare with the following models:
* Comet: http://www.hakank.org/comet/map.co
* Tailor/Essence': http://hakank.org/tailor/map_coloring.eprime
* SICStus: http://hakank.org/sicstus/map_coloring.pl
* ECLiPSe: http://hakank.org/eclipse/map.ecl
* Gecode: http://hakank.org/gecode/map.cpp
* MiniZinc: http://hakank.org/minizinc/map.mzn
* Zinc: http://hakank.org/minizinc/map.zinc
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 ortools.constraint_solver import pywrapcp
def main():
# Create the solver.
solver = pywrapcp.Solver("Map coloring")
#
# data
#
Belgium = 0
Denmark = 1
France = 2
Germany = 3
Netherlands = 4
Luxembourg = 5
n = 6
max_num_colors = 4
# declare variables
color = [solver.IntVar(1, max_num_colors, "x%i" % i) for i in range(n)]
#
# constraints
#
solver.Add(color[Belgium] == 1) # Symmetry breaking
solver.Add(color[France] != color[Belgium])
solver.Add(color[France] != color[Luxembourg])
solver.Add(color[France] != color[Germany])
solver.Add(color[Luxembourg] != color[Germany])
solver.Add(color[Luxembourg] != color[Belgium])
solver.Add(color[Belgium] != color[Netherlands])
solver.Add(color[Belgium] != color[Germany])
solver.Add(color[Germany] != color[Netherlands])
solver.Add(color[Germany] != color[Denmark])
#
# solution and search
#
solution = solver.Assignment()
solution.Add([color[i] for i in range(n)])
collector = solver.AllSolutionCollector(solution)
# collector = solver.FirstSolutionCollector(solution)
# search_log = solver.SearchLog(100, x[0])
solver.Solve(solver.Phase([color[i] for i in range(n)],
solver.INT_VAR_SIMPLE,
solver.ASSIGN_MIN_VALUE),
[collector])
num_solutions = collector.SolutionCount()
print "num_solutions: ", num_solutions
if num_solutions > 0:
for s in range(num_solutions):
colorval = [collector.Value(s, color[i]) for i in range(n)]
print "color:", colorval
print
print "num_solutions:", num_solutions
print "failures:", solver.Failures()
print "branches:", solver.Branches()
print "WallTime:", solver.WallTime()
else:
print "No solutions found"
if __name__ == "__main__":
main()