osrm-backend/routing_algorithms/tsp_farthest_insertion.hpp

/*

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#ifndef TSP_FARTHEST_INSERTION_HPP
#define TSP_FARTHEST_INSERTION_HPP


#include "../data_structures/search_engine.hpp"
#include "../util/string_util.hpp"
#include "../tools/tsp_logs.hpp"

#include <osrm/json_container.hpp>

#include <cstdlib>

#include <algorithm>
#include <string>
#include <vector>
#include <limits>

#include <iostream>

namespace osrm
{
namespace tsp
{

void GetShortestRoundTrip(const int current_loc,
                         const std::vector<EdgeWeight> & dist_table,
                         const int number_of_locations,
                         std::vector<NodeID> & route,
                         int & min_trip_distance,
                         std::vector<NodeID>::iterator & next_insert_point_candidate){
    // for all nodes in the current trip find the best insertion resulting in the shortest path
    // assert min 2 nodes in route
    for (auto from_node = route.begin(); from_node != std::prev(route.end()); ++from_node) {
        const auto to_node = std::next(from_node);

        const auto dist_from = *(dist_table.begin() + (*from_node * number_of_locations) + current_loc);
        const auto dist_to = *(dist_table.begin() + (current_loc * number_of_locations) + *to_node);
        const auto trip_dist = dist_from + dist_to - *(dist_table.begin() + (*from_node * number_of_locations) + *to_node);

        // from all possible insertions to the current trip, choose the shortest of all insertions
        if (trip_dist < min_trip_distance) {
            min_trip_distance = trip_dist;
            next_insert_point_candidate = to_node;
        }
    }
    // check insertion between last and first location too
    auto from_node = std::prev(route.end());
    auto to_node = route.begin();

    auto dist_from = *(dist_table.begin() + (*from_node * number_of_locations) + current_loc);
    auto dist_to = *(dist_table.begin() + (current_loc * number_of_locations) + *to_node);
    auto trip_dist = dist_from + dist_to - *(dist_table.begin() + (*from_node * number_of_locations) + *to_node);
    if (trip_dist < min_trip_distance) {
        min_trip_distance = trip_dist;
        next_insert_point_candidate = to_node;
    }
}

// osrm::tsp::FarthestInsertionTSP(components[k], phantom_node_vector, *result_table, scc_route);
std::vector<NodeID> FarthestInsertionTSP(const std::vector<NodeID> & locations,
                                         const std::size_t number_of_locations,
                                         const std::vector<EdgeWeight> & dist_table) {
    //////////////////////////////////////////////////////////////////////////////////////////////////
    // START FARTHEST INSERTION HERE
    // 1. start at a random round trip of 2 locations
    // 2. find the location that is the farthest away from the visited locations and whose insertion will make the round trip the longest
    // 3. add the found location to the current round trip such that round trip is the shortest
    // 4. repeat 2-3 until all locations are visited
    // 5. DONE!
    //////////////////////////////////////////////////////////////////////////////////////////////////

    std::vector<NodeID> route;
    route.reserve(number_of_locations);

    const int size_of_component = locations.size();
    // tracks which nodes have been already visited
    std::vector<bool> visited(number_of_locations, false);

    auto max_dist = 0;
    auto max_from = -1;
    auto max_to = -1;

    //TODO
    for (auto x : locations) {
        for (auto y : locations) {
            auto xy_dist = *(dist_table.begin() + x * number_of_locations + y);
            if (xy_dist > max_dist) {
                max_dist = xy_dist;
                max_from = x;
                max_to = y;
            }
        }
    }

    visited[max_from] = true;
    visited[max_to] = true;
    route.push_back(max_from);
    route.push_back(max_to);
    // SimpleLogger().Write() << size_of_component;
    // add all other nodes missing (two nodes are already in the initial start trip)
    for (int j = 2; j < size_of_component; ++j) {
        // SimpleLogger().Write() << j << "/" << size_of_component;
        auto farthest_distance = 0;
        auto next_node = -1;
        std::vector<NodeID>::iterator next_insert_point;

        // find unvisited loc i that is the farthest away from all other visited locs
        for (auto i : locations) {
            // find the shortest distance from i to all visited nodes
            if (!visited[i]) {
                auto min_trip_distance = INVALID_EDGE_WEIGHT;
                std::vector<NodeID>::iterator next_insert_point_candidate;

                GetShortestRoundTrip(i, dist_table, number_of_locations, route, min_trip_distance, next_insert_point_candidate);

                // add the location to the current trip such that it results in the shortest total tour
                // SimpleLogger().Write() << "min_trip_distance " << min_trip_distance;
                if (min_trip_distance >= farthest_distance) {
                    farthest_distance = min_trip_distance;
                    next_node = i;
                    next_insert_point = next_insert_point_candidate;
                }
            }
        }
        // SimpleLogger().Write() << "next node " << next_node;
        // mark as visited and insert node
        visited[next_node] = true;
        route.insert(next_insert_point, next_node);
    }
    return route;
}

std::vector<NodeID> FarthestInsertionTSP(const std::size_t number_of_locations,
                                         const std::vector<EdgeWeight> & dist_table) {
    //////////////////////////////////////////////////////////////////////////////////////////////////
    // START FARTHEST INSERTION HERE
    // 1. start at a random round trip of 2 locations
    // 2. find the location that is the farthest away from the visited locations and whose insertion will make the round trip the longest
    // 3. add the found location to the current round trip such that round trip is the shortest
    // 4. repeat 2-3 until all locations are visited
    // 5. DONE!
    //////////////////////////////////////////////////////////////////////////////////////////////////

    std::vector<NodeID> route;
    route.reserve(number_of_locations);

    // tracks which nodes have been already visited
    std::vector<bool> visited(number_of_locations, false);

    // find the pair of location with the biggest distance and make the pair the initial start trip
    const auto index = std::distance(dist_table.begin(), std::max_element(dist_table.begin(), dist_table.end()));
    const int max_from = index / number_of_locations;
    const int max_to = index % number_of_locations;
    visited[max_from] = true;
    visited[max_to] = true;
    route.push_back(max_from);
    route.push_back(max_to);

    // add all other nodes missing (two nodes are already in the initial start trip)
    for (int j = 2; j < number_of_locations; ++j) {
        auto farthest_distance = 0;
        auto next_node = -1;
        //todo move out of loop and overwrite
        std::vector<NodeID>::iterator next_insert_point;

        // find unvisited loc i that is the farthest away from all other visited locs
        for (int i = 0; i < number_of_locations; ++i) {
            if (!visited[i]) {
                auto min_trip_distance = INVALID_EDGE_WEIGHT;
                std::vector<NodeID>::iterator next_insert_point_candidate;

                GetShortestRoundTrip(i, dist_table, number_of_locations, route, min_trip_distance, next_insert_point_candidate);

                // add the location to the current trip such that it results in the shortest total tour
                if (min_trip_distance >= farthest_distance) {
                    farthest_distance = min_trip_distance;
                    next_node = i;
                    next_insert_point = next_insert_point_candidate;
                }
            }
        }

        // mark as visited and insert node
        visited[next_node] = true;
        route.insert(next_insert_point, next_node);
    }
    return route;
}


}
}

#endif // TSP_FARTHEST_INSERTION_HPP