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# 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.

  Faster than the previous versions:
  - http://www.hakank.org/gogle_cp_solver/nqueens.py
  - http://www.hakank.org/gogle_cp_solver/nqueens2.py


  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/
"""
from __future__ import print_function
import sys
from ortools.constraint_solver import pywrapcp


# Create the solver.
solver = pywrapcp.Solver("n-queens")

#
# data
#
print("n:", n)
print("num_sol:", num_sol)
print("print_sol:", print_sol)

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

#
# constraints
#
solver.Add(solver.AllDifferent(q))
solver.Add(solver.AllDifferent([q[i] + i for i in range(n)]))
solver.Add(solver.AllDifferent([q[i] - i for i in range(n)]))

# symmetry breaking
# solver.Add(q[0] == 0)

#
# search
#

db = solver.Phase(q, solver.CHOOSE_MIN_SIZE_LOWEST_MAX,
                  solver.ASSIGN_CENTER_VALUE)

solver.NewSearch(db)
num_solutions = 0
while solver.NextSolution():
  if print_sol:
    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", end=" ")
        else:
          print("_", end=" ")
      print()
    print()
  num_solutions += 1
  if num_sol > 0 and num_solutions >= num_sol:
    break

solver.EndSearch()

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

n = 8
num_sol = 0
print_sol = 1