new python nurses examples in cp/sat and cp
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Laurent Perron
102
examples/python/nurses_cp.py
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102
examples/python/nurses_cp.py
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from __future__ import print_function
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import sys
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from ortools.constraint_solver import pywrapcp
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def main():
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# Creates the solver.
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solver = pywrapcp.Solver("schedule_shifts")
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num_nurses = 4
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num_shifts = 4 # Nurse assigned to shift 0 means not working that day.
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num_days = 7
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# [START]
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# Create shift variables.
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shifts = {}
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for j in range(num_nurses):
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for i in range(num_days):
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shifts[(j, i)] = solver.IntVar(0, num_shifts - 1, "shifts(%i,%i)" % (j, i))
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shifts_flat = [shifts[(j, i)] for j in range(num_nurses) for i in range(num_days)]
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# Create nurse variables.
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nurses = {}
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for j in range(num_shifts):
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for i in range(num_days):
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nurses[(j, i)] = solver.IntVar(0, num_shifts - 1, "shift%d day%d" % (j,i))
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# Set relationships between shifts and nurses.
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for day in range(num_days):
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nurses_for_day = [nurses[(j, day)] for j in range(num_shifts)]
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for j in range(num_nurses):
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s = shifts[(j, day)]
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solver.Add(s.IndexOf(nurses_for_day) == j)
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# Make assignments different on each day
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for i in range(num_days):
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solver.Add(solver.AllDifferent([shifts[(j, i)] for j in range(num_nurses)]))
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solver.Add(solver.AllDifferent([nurses[(j, i)] for j in range(num_shifts)]))
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# Each nurse works 5 or 6 days in a week.
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for j in range(num_nurses):
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solver.Add(solver.Sum([shifts[(j, i)] > 0 for i in range(num_days)]) >= 5)
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solver.Add(solver.Sum([shifts[(j, i)] > 0 for i in range(num_days)]) <= 6)
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# Create works_shift variables. works_shift[(i, j)] is True if nurse
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# i works shift j at least once during the week.
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works_shift = {}
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for i in range(num_nurses):
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for j in range(num_shifts):
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works_shift[(i, j)] = solver.BoolVar('shift%d nurse%d' % (i, j))
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for i in range(num_nurses):
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for j in range(num_shifts):
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solver.Add(works_shift[(i, j)] == solver.Max([shifts[(i, k)] == j for k in range(num_days)]))
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# For each shift (other than 0), at most 2 nurses are assigned to that shift
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# during the week.
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for j in range(1, num_shifts):
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solver.Add(solver.Sum([works_shift[(i, j)] for i in range(num_nurses)]) <= 2)
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# If s nurses works shifts 2 or 3 on, he must also work that shift the previous
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# day or the following day.
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solver.Add(solver.Max(nurses[(2, 0)] == nurses[(2, 1)], nurses[(2, 1)] == nurses[(2, 2)]) == 1)
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solver.Add(solver.Max(nurses[(2, 1)] == nurses[(2, 2)], nurses[(2, 2)] == nurses[(2, 3)]) == 1)
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solver.Add(solver.Max(nurses[(2, 2)] == nurses[(2, 3)], nurses[(2, 3)] == nurses[(2, 4)]) == 1)
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solver.Add(solver.Max(nurses[(2, 3)] == nurses[(2, 4)], nurses[(2, 4)] == nurses[(2, 5)]) == 1)
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solver.Add(solver.Max(nurses[(2, 4)] == nurses[(2, 5)], nurses[(2, 5)] == nurses[(2, 6)]) == 1)
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solver.Add(solver.Max(nurses[(2, 5)] == nurses[(2, 6)], nurses[(2, 6)] == nurses[(2, 0)]) == 1)
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solver.Add(solver.Max(nurses[(2, 6)] == nurses[(2, 0)], nurses[(2, 0)] == nurses[(2, 1)]) == 1)
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solver.Add(solver.Max(nurses[(3, 0)] == nurses[(3, 1)], nurses[(3, 1)] == nurses[(3, 2)]) == 1)
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solver.Add(solver.Max(nurses[(3, 1)] == nurses[(3, 2)], nurses[(3, 2)] == nurses[(3, 3)]) == 1)
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solver.Add(solver.Max(nurses[(3, 2)] == nurses[(3, 3)], nurses[(3, 3)] == nurses[(3, 4)]) == 1)
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solver.Add(solver.Max(nurses[(3, 3)] == nurses[(3, 4)], nurses[(3, 4)] == nurses[(3, 5)]) == 1)
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solver.Add(solver.Max(nurses[(3, 4)] == nurses[(3, 5)], nurses[(3, 5)] == nurses[(3, 6)]) == 1)
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solver.Add(solver.Max(nurses[(3, 5)] == nurses[(3, 6)], nurses[(3, 6)] == nurses[(3, 0)]) == 1)
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solver.Add(solver.Max(nurses[(3, 6)] == nurses[(3, 0)], nurses[(3, 0)] == nurses[(3, 1)]) == 1)
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# Create the decision builder.
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db = solver.Phase(shifts_flat, solver.CHOOSE_FIRST_UNBOUND,
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solver.ASSIGN_MIN_VALUE)
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# Create the solution collector.
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solution = solver.Assignment()
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solution.Add(shifts_flat)
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collector = solver.AllSolutionCollector(solution)
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solver.Solve(db, [collector])
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print("Solutions found:", collector.SolutionCount())
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print("Time:", solver.WallTime(), "ms")
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print()
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# Display a few solutions picked at random.
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a_few_solutions = [859, 2034, 5091, 7003]
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for sol in a_few_solutions:
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print("Solution number" , sol, '\n')
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for i in range(num_days):
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print("Day", i)
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for j in range(num_nurses):
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print("Nurse", j, "assigned to task",
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collector.Value(sol, shifts[(j, i)]))
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print()
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if __name__ == "__main__":
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main()
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131
examples/python/nurses_sat.py
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131
examples/python/nurses_sat.py
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# Copyright 2010-2017 Google
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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from __future__ import print_function
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import sys
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from ortools.sat.python import cp_model
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class NursesPartialSolutionPrinter(cp_model.CpSolverSolutionCallback):
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"""Print intermediate solutions."""
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def __init__(self, shifts, num_nurses, num_days, num_shifts, sols):
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self.__shifts = shifts
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self.__num_nurses = num_nurses
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self.__num_days = num_days
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self.__num_shifts = num_shifts
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self.__solutions = set(sols)
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self.__solution_count = 0
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def NewSolution(self):
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self.__solution_count += 1
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if self.__solution_count in self.__solutions:
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print('Solution #%i' % self.__solution_count)
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for d in range(self.__num_days):
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print('Day #%i' % d)
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for n in range(self.__num_nurses):
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for s in range(self.__num_shifts):
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if self.Value(self.__shifts[(n, d, s)]):
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print(' Nurse #%i is working shift #%i' % (n, s))
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print()
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def SolutionCount(self):
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return self.__solution_count
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def main():
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# Data.
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num_nurses = 4
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num_shifts = 4 # Nurse assigned to shift 0 means not working that day.
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num_days = 7
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all_nurses = range(num_nurses)
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all_shifts = range(num_shifts)
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all_working_shifts = range(1, num_shifts)
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all_days = range(num_days)
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# Creates the model.
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model = cp_model.CpModel()
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# Creates shift variables.
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# shifts[(n, d, s)]: nurse 'n' works shift 's' on day 'd'.
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shifts = {}
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for n in all_nurses:
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for d in all_days:
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for s in all_shifts:
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shifts[(n, d, s)] = model.NewBoolVar('shift_n%id%is%i' % (n, d, s))
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# Makes assignments different on each day, that is each shift is assigned at
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# most one nurse. As we have the same number of nurses and shifts, then each
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# day, each shift is assigned to exactly one nurse.
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for d in all_days:
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for s in all_shifts:
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model.Add(sum(shifts[(n, d, s)] for n in all_nurses) == 1)
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# Nurses do 1 shift per day.
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for n in all_nurses:
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for d in all_days:
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model.Add(sum(shifts[(n, d, s)] for s in all_shifts) == 1)
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# Each nurse works 5 or 6 days in a week.
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# That is each nurse works shift 0 at most 2 times.
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for n in all_nurses:
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model.Add(sum(shifts[(n, d, 0)] for d in all_days) <= 2)
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# works_shift[(n, s)] is 1 if nurse n works shift s at least one day in
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# the week.
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works_shift = {}
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for n in all_nurses:
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for s in all_shifts:
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works_shift[(n, s)] = model.NewBoolVar('works_shift_n%is%i' % (n, s))
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model.AddMaxEquality(works_shift[(n, s)],
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[shifts[(n, d, s)] for d in all_days])
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# For each shift, at most 2 nurses are assigned to that shift during the week.
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for s in all_working_shifts:
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model.Add(sum(works_shift[(n, s)] for n in all_nurses) <= 2)
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# If s nurses works shifts 2 or 3 on, she must also work that shift the
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# previous day or the following day.
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# This means that on a given day and shift, either she does not work that
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# shift on that day, or she works that shift on the day before, or the day
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# after.
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for n in all_nurses:
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for s in [2, 3]:
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for d in all_days:
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yesterday = (d - 1) % num_days
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tomorrow = (d + 1) % num_days
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model.AddBoolOr([shifts[(n, yesterday, s)], shifts[(n, d, s)].Not(),
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shifts[(n, tomorrow, s)]])
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# Creates the solver and solve.
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solver = cp_model.CpSolver()
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# Display a few solutions picked at random.
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a_few_solutions = [859, 2034, 5091, 7003]
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solution_printer = NursesPartialSolutionPrinter(shifts, num_nurses,
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num_days, num_shifts,
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a_few_solutions)
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status = solver.SearchForAllSolutions(model, solution_printer)
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# Statistics.
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print()
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print('Statistics')
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print(' - conflicts : %i' % solver.NumConflicts())
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print(' - branches : %i' % solver.NumBranches())
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print(' - wall time : %f ms' % solver.WallTime())
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print(' - solutions found : %i' % solution_printer.SolutionCount())
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if __name__ == "__main__":
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main()
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