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