Tsp.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.
///   A description of the problem can be found here:
///   http://en.wikipedia.org/wiki/Travelling_salesperson_problem.
/// </summary>
public class Tsp
{
    // [START data_model]
    class DataModel
    {
        // Constructor:
        public DataModel()
        {
            // Convert locations in meters using a city block dimension of 114m x 80m.
            for (int i = 0; i < Locations.GetLength(0); i++)
            {
                Locations[i, 0] *= 114;
                Locations[i, 1] *= 80;
            }
        }
        public int[,] Locations = { { 4, 4 }, { 2, 0 }, { 8, 0 }, { 0, 1 }, { 1, 1 }, { 5, 2 },
                                    { 7, 2 }, { 3, 3 }, { 6, 3 }, { 5, 5 }, { 8, 5 }, { 1, 6 },
                                    { 2, 6 }, { 3, 7 }, { 6, 7 }, { 0, 8 }, { 7, 8 } };
        public int VehicleNumber = 1;
        public int Depot = 0;
    };
    // [END data_model]

    // [START manhattan_distance]
    /// <summary>
    ///   Manhattan distance implemented as a callback. It uses an array of
    ///   positions and computes the Manhattan distance between the two
    ///   positions of two different indices.
    /// </summary>
    class ManhattanDistance
    {
        public ManhattanDistance(in DataModel data, in RoutingIndexManager manager)
        {
            // precompute distance between location to have distance callback in O(1)
            int locationNumber = data.Locations.GetLength(0);
            distancesMatrix_ = new long[locationNumber, locationNumber];
            indexManager_ = manager;
            for (int fromNode = 0; fromNode < locationNumber; fromNode++)
            {
                for (int toNode = 0; toNode < locationNumber; toNode++)
                {
                    if (fromNode == toNode)
                        distancesMatrix_[fromNode, toNode] = 0;
                    else
                        distancesMatrix_[fromNode, toNode] =
                            Math.Abs(data.Locations[toNode, 0] - data.Locations[fromNode, 0]) +
                            Math.Abs(data.Locations[toNode, 1] - data.Locations[fromNode, 1]);
                }
            }
        }

        /// <summary>
        ///   Returns the manhattan distance between the two nodes
        /// </summary>
        public long Call(long fromIndex, long toIndex)
        {
            // Convert from routing variable Index to distance matrix NodeIndex.
            int fromNode = indexManager_.IndexToNode(fromIndex);
            int toNode = indexManager_.IndexToNode(toIndex);
            return distancesMatrix_[fromNode, toNode];
        }
        private long[,] distancesMatrix_;
        private RoutingIndexManager indexManager_;
    };
    // [END manhattan_distance]

    // [START solution_printer]
    /// <summary>
    ///   Print the solution.
    /// </summary>
    static void PrintSolution(in RoutingModel routing, in RoutingIndexManager manager, in Assignment solution)
    {
        Console.WriteLine("Objective: {0}", solution.ObjectiveValue());
        // Inspect solution.
        Console.WriteLine("Route for Vehicle 0:");
        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("Distance of the route: {0}m", 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.Locations.GetLength(0), data.VehicleNumber, data.Depot);
        // [END index_manager]

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

        // Create and register a transit callback.
        // [START transit_callback]
        var distanceCallback = new ManhattanDistance(data, manager);
        int transitCallbackIndex = routing.RegisterTransitCallback(distanceCallback.Call);
        // [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]