# Copyright 2010 Hakan Kjellerstrand hakank@gmail.com
#
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#
# Unless required by applicable law or agreed to in writing, software
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and

"""

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)
"""
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
#
for i in range(n):
for j in range(i):
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):

# symmetry breaking

#
# solution and search
#
solution = solver.Assignment()

# 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)
main(n)