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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.
"""

  Bus scheduling in Google CP Solver.


  Problem from Taha "Introduction to Operations Research", page 58.

  This is a slightly more general model than Taha's.

  Compare with the following models:
  * MiniZinc: http://www.hakank.org/minizinc/bus_scheduling.mzn
  * Comet   : http://www.hakank.org/comet/bus_schedule.co
  * ECLiPSe : http://www.hakank.org/eclipse/bus_schedule.ecl
  * Gecode  : http://www.hakank.org/gecode/bus_schedule.cpp
  * Tailor/Essence'  : http://www.hakank.org/tailor/bus_schedule.eprime
  * SICStus: http://hakank.org/sicstus/bus_schedule.pl

  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("Bus scheduling")

# data
time_slots = 6
demands = [8, 10, 7, 12, 4, 4]
max_num = sum(demands)

# declare variables
x = [solver.IntVar(0, max_num, "x%i" % i) for i in range(time_slots)]
num_buses = solver.IntVar(0, max_num, "num_buses")

#
# constraints
#
solver.Add(num_buses == solver.Sum(x))

# Meet the demands for this and the next time slot
for i in range(time_slots - 1):
  solver.Add(x[i] + x[i + 1] >= demands[i])

# The demand "around the clock"
solver.Add(x[time_slots - 1] + x[0] == demands[time_slots - 1])

if num_buses_check > 0:
  solver.Add(num_buses == num_buses_check)

#
# solution and search
#
solution = solver.Assignment()
solution.Add(x)
solution.Add(num_buses)

collector = solver.AllSolutionCollector(solution)
cargs = [collector]

# objective
if num_buses_check == 0:
  objective = solver.Minimize(num_buses, 1)
  cargs.extend([objective])

solver.Solve(
    solver.Phase(x, solver.CHOOSE_FIRST_UNBOUND, solver.ASSIGN_MIN_VALUE),
    cargs)

num_solutions = collector.SolutionCount()
num_buses_check_value = 0
for s in range(num_solutions):
  print("x:", [collector.Value(s, x[i]) for i in range(len(x))], end=" ")
  num_buses_check_value = collector.Value(s, num_buses)
  print(" num_buses:", num_buses_check_value)

print()
print("num_solutions:", num_solutions)
print("failures:", solver.Failures())
print("branches:", solver.Branches())
print("WallTime:", solver.WallTime())
print()
if num_buses_check == 0:
  return num_buses_check_value