# Copyright 2010 Hakan Kjellerstrand hakank@bonetmail.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.
"""
Organizing a day in Google CP Solver.
Simple scheduling problem.
Problem formulation from ECLiPSe:
Slides on (Finite Domain) Constraint Logic Programming, page 38f
http://eclipse-clp.org/reports/eclipse.ppt
Compare with the following models:
* MiniZinc: http://www.hakank.org/minizinc/organize_day.mzn
* Comet: http://www.hakank.org/comet/organize_day.co
* Gecode: http://hakank.org/gecode/organize_day.cpp
This model was created by Hakan Kjellerstrand (hakank@bonetmail.com)
Also see my other Google CP Solver models:
http://www.hakank.org/google_or_tools/
"""
import sys
from ortools.constraint_solver import pywrapcp
#
# No overlapping of tasks s1 and s2
#
def no_overlap(solver, s1, d1, s2, d2):
b1 = solver.IsLessOrEqualVar(s1 + d1, s2) # s1 + d1 <= s2
b2 = solver.IsLessOrEqualVar(s2 + d2, s1) # s2 + d2 <= s1
solver.Add(b1 + b2 >= 1)
def main():
# Create the solver.
solver = pywrapcp.Solver('Organizing a day')
#
# data
#
n = 4
tasks = range(n)
work, mail, shop, bank = tasks
durations = [4, 1, 2, 1]
# task [i,0] must be finished before task [i,1]
before_tasks = [
[bank, shop],
[mail, work]
]
# the valid times of the day
begin = 9
end = 17
#
# declare variables
#
begins = [solver.IntVar(begin, end, 'begins[%i]% % i') for i in tasks]
ends = [solver.IntVar(begin, end, 'ends[%i]% % i') for i in tasks]
#
# constraints
#
for i in tasks:
solver.Add(ends[i] == begins[i] + durations[i])
for i in tasks:
for j in tasks:
if i < j:
no_overlap(solver,
begins[i], durations[i],
begins[j], durations[j])
# specific constraints
for (before, after) in before_tasks:
solver.Add(ends[before] <= begins[after])
solver.Add(begins[work] >= 11)
#
# solution and search
#
db = solver.Phase(begins + ends,
solver.INT_VAR_DEFAULT,
solver.INT_VALUE_DEFAULT)
solver.NewSearch(db)
num_solutions = 0
while solver.NextSolution():
num_solutions += 1
print 'begins:', [begins[i].Value() for i in tasks]
print 'ends:', [ends[i].Value() for i in tasks]
print
print 'num_solutions:', num_solutions
print 'failures:', solver.Failures()
print 'branches:', solver.Branches()
print 'WallTime:', solver.WallTime(), 'ms'
if __name__ == '__main__':
main()