1. CSPlib
  2. Problems
  3. prob054
  4. Models
  5. nqueens2_ortools.py

054: N-Queens

Download
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
# Copyright 2010 Hakan Kjellerstrand hakank@gmail.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.
 
"""
 
  n-queens problem in Google CP Solver.
 
  N queens problem.
 
  This version use NewSearch()/NextSolution() for looping through
  the solutions.
 
  This model was created by Hakan Kjellerstrand (hakank@gmail.com)
  Also see my other Google CP Solver models: http://www.hakank.org/google_or_tools/
"""
import sys, string
from constraint_solver import pywrapcp
 
 
def main(n=8):
    # Create the solver.
    solver = pywrapcp.Solver('n-queens')
 
    #
    # data
    #
    # n = 8 # size of board (n x n)
 
    # declare variables
    q = [solver.IntVar(0,n-1, 'x%i' % i) for i in range(n)]
 
    #
    # constraints
    #
    solver.Add(solver.AllDifferent(q))
    for i in range(n):
        for j in range(i):
            solver.Add(q[i] != q[j])
            solver.Add(q[i] + i != q[j] + j)
            solver.Add(q[i] - i != q[j] - j)
 
    # for i in range(n):
    #     for j in range(i):
    #         solver.Add(abs(q[i]-q[j]) != abs(i-j))
 
    # symmetry breaking
    # solver.Add(q[0] == 0)
 
 
    #
    # solution and search
    #
    solution = solver.Assignment()
    solution.Add([q[i] for i in range(n)])
 
 
    # db: DecisionBuilder
    db = solver.Phase([q[i] for i in range(n)],
                      # solver.CHOOSE_FIRST_UNBOUND,
                      solver.CHOOSE_MIN_SIZE_LOWEST_MAX,
                      solver.ASSIGN_CENTER_VALUE)
 
    solver.NewSearch(db)
    num_solutions = 0
    while solver.NextSolution():
        qval = [q[i].Value() for i in range(n)]
        print "q:", qval
        for i in range(n):
            for j in range(n):
                if qval[i] == j:
                    print "Q",
                else:
                    print "_",
            print
        print
        num_solutions += 1
    solver.EndSearch()
 
    print
    print "num_solutions:", num_solutions
    print "failures:", solver.Failures()
    print "branches:", solver.Branches()
    print "WallTime:", solver.WallTime()
 
 
n = 8
if __name__ == '__main__':
    if len(sys.argv) > 1:
        n = string.atoi(sys.argv[1])
    main(n)