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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.

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


# 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", end=" ")
      else:
        print("_", end=" ")
    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