100 lines
2.7 KiB
Python
100 lines
2.7 KiB
Python
# Copyright 2010 Hakan Kjellerstrand hakank@bonetmail.com
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""
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n-queens problem in Google CP Solver.
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N queens problem.
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This model was created by Hakan Kjellerstrand (hakank@bonetmail.com)
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Also see my other Google CP Solver models: http://www.hakank.org/google_or_tools/
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"""
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from constraint_solver import pywrapcp
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def main(n=8):
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# Create the solver.
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solver = pywrapcp.Solver('n-queens')
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#
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# data
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#
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# n = 8 # size of board (n x n)
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# declare variables
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q = [solver.IntVar(0,n-1, 'x%i' % i) for i in range(n)]
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#
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# constraints
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#
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solver.Add(solver.AllDifferent(q))
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for i in range(n):
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for j in range(i):
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solver.Add(q[i] != q[j])
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solver.Add(q[i] + i != q[j] + j)
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solver.Add(q[i] - i != q[j] - j)
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# for i in range(n):
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# for j in range(i):
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# solver.Add(abs(q[i]-q[j]) != abs(i-j))
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# symmetry breaking
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# solver.Add(q[0] == 0)
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#
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# solution and search
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#
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solution = solver.Assignment()
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solution.Add([q[i] for i in range(n)])
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collector = solver.AllSolutionCollector(solution)
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# collector = solver.FirstSolutionCollector(solution)
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# search_log = solver.SearchLog(100, x[0])
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solver.Solve(solver.Phase([q[i] for i in range(n)],
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solver.INT_VAR_SIMPLE,
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solver.ASSIGN_MIN_VALUE),
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[collector])
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num_solutions = collector.SolutionCount()
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print "num_solutions: ", num_solutions
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if num_solutions > 0:
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for s in range(num_solutions):
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qval = [collector.Value(s, q[i]) for i in range(n)]
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print "q:", qval
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for i in range(n):
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for j in range(n):
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if qval[i] == j:
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print "Q",
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else:
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print "_",
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print
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print
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print
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print "num_solutions:", num_solutions
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print "failures:", solver.Failures()
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print "branches:", solver.Branches()
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print "WallTime:", solver.WallTime()
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else:
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print "No solutions found"
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n = 8
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if __name__ == '__main__':
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main(n)
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