vrp_drop_nodes.cc

Simple VRP example.

// Copyright 2010-2025 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]
#include <cstdint>
#include <cstdlib>
#include <sstream>
#include <vector>
 
#include "google/protobuf/duration.pb.h"
#include "ortools/base/logging.h"
#include "ortools/constraint_solver/constraint_solver.h"
#include "ortools/constraint_solver/routing.h"
#include "ortools/constraint_solver/routing_enums.pb.h"
#include "ortools/constraint_solver/routing_index_manager.h"
#include "ortools/constraint_solver/routing_parameters.h"
// [END import]
 
namespace operations_research {
// [START data_model]
struct DataModel {
  const std::vector<std::vector<int64_t>> distance_matrix{
      {0, 548, 776, 696, 582, 274, 502, 194, 308, 194, 536, 502, 388, 354, 468,
       776, 662},
      {548, 0, 684, 308, 194, 502, 730, 354, 696, 742, 1084, 594, 480, 674,
       1016, 868, 1210},
      {776, 684, 0, 992, 878, 502, 274, 810, 468, 742, 400, 1278, 1164, 1130,
       788, 1552, 754},
      {696, 308, 992, 0, 114, 650, 878, 502, 844, 890, 1232, 514, 628, 822,
       1164, 560, 1358},
      {582, 194, 878, 114, 0, 536, 764, 388, 730, 776, 1118, 400, 514, 708,
       1050, 674, 1244},
      {274, 502, 502, 650, 536, 0, 228, 308, 194, 240, 582, 776, 662, 628, 514,
       1050, 708},
      {502, 730, 274, 878, 764, 228, 0, 536, 194, 468, 354, 1004, 890, 856, 514,
       1278, 480},
      {194, 354, 810, 502, 388, 308, 536, 0, 342, 388, 730, 468, 354, 320, 662,
       742, 856},
      {308, 696, 468, 844, 730, 194, 194, 342, 0, 274, 388, 810, 696, 662, 320,
       1084, 514},
      {194, 742, 742, 890, 776, 240, 468, 388, 274, 0, 342, 536, 422, 388, 274,
       810, 468},
      {536, 1084, 400, 1232, 1118, 582, 354, 730, 388, 342, 0, 878, 764, 730,
       388, 1152, 354},
      {502, 594, 1278, 514, 400, 776, 1004, 468, 810, 536, 878, 0, 114, 308,
       650, 274, 844},
      {388, 480, 1164, 628, 514, 662, 890, 354, 696, 422, 764, 114, 0, 194, 536,
       388, 730},
      {354, 674, 1130, 822, 708, 628, 856, 320, 662, 388, 730, 308, 194, 0, 342,
       422, 536},
      {468, 1016, 788, 1164, 1050, 514, 514, 662, 320, 274, 388, 650, 536, 342,
       0, 764, 194},
      {776, 868, 1552, 560, 674, 1050, 1278, 742, 1084, 810, 1152, 274, 388,
       422, 764, 0, 798},
      {662, 1210, 754, 1358, 1244, 708, 480, 856, 514, 468, 354, 844, 730, 536,
       194, 798, 0},
  };
  // [START demands_capacities]
  const std::vector<int64_t> demands{
      0, 1, 1, 3, 6, 3, 6, 8, 8, 1, 2, 1, 2, 6, 6, 8, 8,
  };
  const std::vector<int64_t> vehicle_capacities{15, 15, 15, 15};
  // [END demands_capacities]
  const int num_vehicles = 4;
  const RoutingIndexManager::NodeIndex depot{0};
};
// [END data_model]
 
// [START solution_printer]
void PrintSolution(const DataModel& data, const RoutingIndexManager& manager,
                   const RoutingModel& routing, const Assignment& solution) {
  // Display dropped nodes.
  std::ostringstream dropped_nodes;
  for (int64_t node = 0; node < routing.Size(); ++node) {
    if (routing.IsStart(node) || routing.IsEnd(node)) continue;
    if (solution.Value(routing.NextVar(node)) == node) {
      dropped_nodes << " " << manager.IndexToNode(node).value();
    }
  }
  LOG(INFO) << "Dropped nodes:" << dropped_nodes.str();
  // Display routes
  int64_t total_distance{0};
  int64_t total_load{0};
  for (int vehicle_id = 0; vehicle_id < data.num_vehicles; ++vehicle_id) {
    if (!routing.IsVehicleUsed(solution, vehicle_id)) {
      continue;
    }
    int64_t index = routing.Start(vehicle_id);
    LOG(INFO) << "Route for Vehicle " << vehicle_id << ":";
    int64_t route_distance{0};
    int64_t route_load{0};
    std::ostringstream route;
    while (!routing.IsEnd(index)) {
      const int node_index = manager.IndexToNode(index).value();
      route_load += data.demands[node_index];
      route << node_index << " Load(" << route_load << ") -> ";
      const int64_t previous_index = index;
      index = solution.Value(routing.NextVar(index));
      route_distance += routing.GetArcCostForVehicle(previous_index, index,
                                                     int64_t{vehicle_id});
    }
    LOG(INFO) << route.str() << manager.IndexToNode(index).value();
    LOG(INFO) << "Distance of the route: " << route_distance << "m";
    LOG(INFO) << "Load of the route: " << route_load;
    total_distance += route_distance;
    total_load += route_load;
  }
  LOG(INFO) << "Total distance of all routes: " << total_distance << "m";
  LOG(INFO) << "Total load of all routes: " << total_load;
  LOG(INFO) << "";
  LOG(INFO) << "Advanced usage:";
  LOG(INFO) << "Problem solved in " << routing.solver()->wall_time() << "ms";
}
// [END solution_printer]
 
void VrpDropNodes() {
  // Instantiate the data problem.
  // [START data]
  DataModel data;
  // [END data]
 
  // Create Routing Index Manager
  // [START index_manager]
  RoutingIndexManager manager(data.distance_matrix.size(), data.num_vehicles,
                              data.depot);
  // [END index_manager]
 
  // Create Routing Model.
  // [START routing_model]
  RoutingModel routing(manager);
  // [END routing_model]
 
  // Create and register a transit callback.
  // [START transit_callback]
  const int transit_callback_index = routing.RegisterTransitCallback(
      [&data, &manager](const int64_t from_index,
                        const int64_t to_index) -> int64_t {
        // Convert from routing variable Index to distance matrix NodeIndex.
        const int from_node = manager.IndexToNode(from_index).value();
        const int to_node = manager.IndexToNode(to_index).value();
        return data.distance_matrix[from_node][to_node];
      });
  // [END transit_callback]
 
  // Define cost of each arc.
  // [START arc_cost]
  routing.SetArcCostEvaluatorOfAllVehicles(transit_callback_index);
  // [END arc_cost]
 
  // Add Capacity constraint.
  // [START capacity_constraint]
  const int demand_callback_index = routing.RegisterUnaryTransitCallback(
      [&data, &manager](const int64_t from_index) -> int64_t {
        // Convert from routing variable Index to demand NodeIndex.
        const int from_node = manager.IndexToNode(from_index).value();
        return data.demands[from_node];
      });
  routing.AddDimensionWithVehicleCapacity(
      demand_callback_index,    // transit callback index
      int64_t{0},               // null capacity slack
      data.vehicle_capacities,  // vehicle maximum capacities
      true,                     // start cumul to zero
      "Capacity");
  // Allow to drop nodes.
  int64_t penalty{1000};
  for (int i = 1; i < data.distance_matrix.size(); ++i) {
    routing.AddDisjunction(
        {manager.NodeToIndex(RoutingIndexManager::NodeIndex(i))}, penalty);
  }
  // [END capacity_constraint]
 
  // Setting first solution heuristic.
  // [START parameters]
  RoutingSearchParameters search_parameters = DefaultRoutingSearchParameters();
  search_parameters.set_first_solution_strategy(
      FirstSolutionStrategy::PATH_CHEAPEST_ARC);
  search_parameters.set_local_search_metaheuristic(
      LocalSearchMetaheuristic::GUIDED_LOCAL_SEARCH);
  search_parameters.mutable_time_limit()->set_seconds(1);
  // [END parameters]
 
  // Solve the problem.
  // [START solve]
  const Assignment* solution = routing.SolveWithParameters(search_parameters);
  // [END solve]
 
  // Print solution on console.
  // [START print_solution]
  PrintSolution(data, manager, routing, *solution);
  // [END print_solution]
}
}  // namespace operations_research
 
int main(int /*argc*/, char* /*argv*/[]) {
  operations_research::VrpDropNodes();
  return EXIT_SUCCESS;
}
// [END program]