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bus_schedule.cs
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bus_schedule.cs
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//
// Copyright 2012 Hakan Kjellerstrand
//
// 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.
using System;
using System.Collections;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using Google.OrTools.ConstraintSolver;
public class BusSchedule
{
/**
*
* Bus scheduling.
*
* Minimize number of buses in timeslots.
*
* Problem from Taha "Introduction to Operations Research", page 58.
*
* This is a slightly more general model than Taha's.
*
* Also see, http://www.hakank.org/or-tools/bus_schedule.py
*
*/
private static long Solve(long num_buses_check = 0)
{
Solver solver = new Solver("BusSchedule");
//
// data
//
int time_slots = 6;
int[] demands = {8, 10, 7, 12, 4, 4};
int max_num = demands.Sum();
//
// Decision variables
//
// How many buses start the schedule at time slot t
IntVar[] x = solver.MakeIntVarArray(time_slots, 0, max_num, "x");
// Total number of buses
IntVar num_buses = x.Sum().VarWithName("num_buses");
//
// Constraints
//
// Meet the demands for this and the next time slot.
for(int i = 0; i < time_slots - 1; i++) {
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] == 0);
// For showing all solutions of minimal number of buses
if (num_buses_check > 0) {
solver.Add(num_buses == num_buses_check);
}
//
// Search
//
DecisionBuilder db = solver.MakePhase(x,
Solver.CHOOSE_FIRST_UNBOUND,
Solver.ASSIGN_MIN_VALUE);
if (num_buses_check == 0) {
// Minimize num_buses
OptimizeVar obj = num_buses.Minimize(1);
solver.NewSearch(db, obj);
} else {
solver.NewSearch(db);
}
long result = 0;
while (solver.NextSolution()) {
result = num_buses.Value();
Console.Write("x: ");
for(int i = 0; i < time_slots; i++) {
Console.Write("{0,2} ", x[i].Value());
}
Console.WriteLine("num_buses: " + num_buses.Value());
}
Console.WriteLine("\nSolutions: {0}", solver.Solutions());
Console.WriteLine("WallTime: {0}ms", solver.WallTime());
Console.WriteLine("Failures: {0}", solver.Failures());
Console.WriteLine("Branches: {0} ", solver.Branches());
solver.EndSearch();
return result;
}
public static void Main(String[] args)
{
Console.WriteLine("Check for minimum number of buses: ");
long num_buses = Solve();
Console.WriteLine("\n... got {0} as minimal value.", num_buses);
Console.WriteLine("\nAll solutions: ", num_buses);
num_buses = Solve(num_buses);
}
}