TspCities.cs

// Copyright 2010-2024 Google LLC
// 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.

// [START program]
// [START import]
using System;
using System.Collections.Generic;
using Google.OrTools.ConstraintSolver;
// [END import]

/// <summary>
///   Minimal TSP using distance matrix.
/// </summary>
public class TspCities
{
    // [START data_model]
    class DataModel
    {
        public long[,] DistanceMatrix = {
            { 0, 2451, 713, 1018, 1631, 1374, 2408, 213, 2571, 875, 1420, 2145, 1972 },
            { 2451, 0, 1745, 1524, 831, 1240, 959, 2596, 403, 1589, 1374, 357, 579 },
            { 713, 1745, 0, 355, 920, 803, 1737, 851, 1858, 262, 940, 1453, 1260 },
            { 1018, 1524, 355, 0, 700, 862, 1395, 1123, 1584, 466, 1056, 1280, 987 },
            { 1631, 831, 920, 700, 0, 663, 1021, 1769, 949, 796, 879, 586, 371 },
            { 1374, 1240, 803, 862, 663, 0, 1681, 1551, 1765, 547, 225, 887, 999 },
            { 2408, 959, 1737, 1395, 1021, 1681, 0, 2493, 678, 1724, 1891, 1114, 701 },
            { 213, 2596, 851, 1123, 1769, 1551, 2493, 0, 2699, 1038, 1605, 2300, 2099 },
            { 2571, 403, 1858, 1584, 949, 1765, 678, 2699, 0, 1744, 1645, 653, 600 },
            { 875, 1589, 262, 466, 796, 547, 1724, 1038, 1744, 0, 679, 1272, 1162 },
            { 1420, 1374, 940, 1056, 879, 225, 1891, 1605, 1645, 679, 0, 1017, 1200 },
            { 2145, 357, 1453, 1280, 586, 887, 1114, 2300, 653, 1272, 1017, 0, 504 },
            { 1972, 579, 1260, 987, 371, 999, 701, 2099, 600, 1162, 1200, 504, 0 },
        };
        public int VehicleNumber = 1;
        public int Depot = 0;
    };
    // [END data_model]

    // [START solution_printer]
    /// <summary>
    ///   Print the solution.
    /// </summary>
    static void PrintSolution(in RoutingModel routing, in RoutingIndexManager manager, in Assignment solution)
    {
        Console.WriteLine("Objective: {0} miles", solution.ObjectiveValue());
        // Inspect solution.
        Console.WriteLine("Route:");
        long routeDistance = 0;
        var index = routing.Start(0);
        while (routing.IsEnd(index) == false)
        {
            Console.Write("{0} -> ", manager.IndexToNode((int)index));
            var previousIndex = index;
            index = solution.Value(routing.NextVar(index));
            routeDistance += routing.GetArcCostForVehicle(previousIndex, index, 0);
        }
        Console.WriteLine("{0}", manager.IndexToNode((int)index));
        Console.WriteLine("Route distance: {0}miles", routeDistance);
    }
    // [END solution_printer]

    public static void Main(String[] args)
    {
        // Instantiate the data problem.
        // [START data]
        DataModel data = new DataModel();
        // [END data]

        // Create Routing Index Manager
        // [START index_manager]
        RoutingIndexManager manager =
            new RoutingIndexManager(data.DistanceMatrix.GetLength(0), data.VehicleNumber, data.Depot);
        // [END index_manager]

        // Create Routing Model.
        // [START routing_model]
        RoutingModel routing = new RoutingModel(manager);
        // [END routing_model]

        // [START transit_callback]
        int transitCallbackIndex = routing.RegisterTransitCallback((long fromIndex, long toIndex) =>
                                                                   {
                                                                       // Convert from routing variable Index to
                                                                       // distance matrix NodeIndex.
                                                                       var fromNode = manager.IndexToNode(fromIndex);
                                                                       var toNode = manager.IndexToNode(toIndex);
                                                                       return data.DistanceMatrix[fromNode, toNode];
                                                                   });
        // [END transit_callback]

        // Define cost of each arc.
        // [START arc_cost]
        routing.SetArcCostEvaluatorOfAllVehicles(transitCallbackIndex);
        // [END arc_cost]

        // Setting first solution heuristic.
        // [START parameters]
        RoutingSearchParameters searchParameters =
            operations_research_constraint_solver.DefaultRoutingSearchParameters();
        searchParameters.FirstSolutionStrategy = FirstSolutionStrategy.Types.Value.PathCheapestArc;
        // [END parameters]

        // Solve the problem.
        // [START solve]
        Assignment solution = routing.SolveWithParameters(searchParameters);
        // [END solve]

        // Print solution on console.
        // [START print_solution]
        PrintSolution(routing, manager, solution);
        // [END print_solution]
    }
}
// [END program]