SteinerTreePreprocessing.h

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#pragma once
 
#include <ogdf/basic/BoundedQueue.h>
#include <ogdf/basic/SubsetEnumerator.h>
#include <ogdf/graphalg/MinSteinerTreeMehlhorn.h>
#include <ogdf/graphalg/MinSteinerTreeTakahashi.h>
#include <ogdf/graphalg/SteinerTreeLowerBoundDualAscent.h>
#include <ogdf/graphalg/steiner_tree/HeavyPathDecomposition.h>
 
#include <forward_list>
#include <memory>
#include <set>
#include <unordered_map>
 
namespace ogdf {
 
// Helpers:
namespace steiner_tree {
class UnorderedNodePairHasher {
public:
    int operator()(const NodePair& v) const {
        return static_cast<int>((static_cast<long long>(min(v.source->index(), v.target->index()) + 11)
                                        * (max(v.source->index(), v.target->index()) + 73))
                % 700001);
    }
};
 
class UnorderedNodePairEquality {
public:
    bool operator()(const NodePair& pair1, const NodePair& pair2) const {
        return (pair1.source == pair2.source && pair1.target == pair2.target)
                || (pair1.source == pair2.target && pair1.target == pair2.source);
    }
};
 
}
 
template<typename T>
class SteinerTreePreprocessing {
protected:
    const EdgeWeightedGraph<T>& m_origGraph; 
    const List<node>& m_origTerminals; 
    const NodeArray<bool>& m_origIsTerminal; 
    const EpsilonTest m_eps;
 
    EdgeWeightedGraph<T> m_copyGraph; 
    List<node> m_copyTerminals; 
    NodeArray<bool> m_copyIsTerminal; 
 
    T m_costAlreadyInserted; 
 
    NodeArray<int> m_nodeSonsListIndex; 
    EdgeArray<int> m_edgeSonsListIndex; 
    std::vector<std::vector<int>> m_sonsList; 
 
    std::unique_ptr<MinSteinerTreeModule<T>> m_costUpperBoundAlgorithm;
 
public:
    SteinerTreePreprocessing(const EdgeWeightedGraph<T>& wg, const List<node>& terminals,
            const NodeArray<bool>& isTerminal);
 
    T solve(MinSteinerTreeModule<T>& mst, EdgeWeightedGraphCopy<T>*& finalSteinerTree) {
        finalSteinerTree = new EdgeWeightedGraphCopy<T>;
        // reductions generate new nodes and edges, which may inflate the internal structure
        if (m_copyGraph.maxNodeIndex() <= m_copyGraph.numberOfNodes() + 5
                && m_copyGraph.maxEdgeIndex()
                        <= m_copyGraph.numberOfEdges() + 10) { // within inflate tolerance
            EdgeWeightedGraphCopy<T>* reducedSolution = nullptr;
            T cost = mst.call(m_copyGraph, m_copyTerminals, m_copyIsTerminal, reducedSolution);
            cost += costEdgesAlreadyInserted();
            computeOriginalSolution(*reducedSolution, *finalSteinerTree);
            delete reducedSolution;
            return cost;
        }
 
        // make a compact copy
        EdgeWeightedGraph<T> ccGraph;
        NodeArray<node> nCopy(m_copyGraph, nullptr);
        EdgeArray<edge> eCopy(m_copyGraph, nullptr);
        List<node> ccTerminals;
        NodeArray<bool> ccIsTerminal(ccGraph, false);
        for (node v : m_copyGraph.nodes) {
            nCopy[v] = ccGraph.newNode();
        }
        for (edge e : m_copyGraph.edges) {
            eCopy[e] = ccGraph.newEdge(nCopy[e->source()], nCopy[e->target()], m_copyGraph.weight(e));
        }
        for (node t : m_copyTerminals) {
            const node tC = nCopy[t];
            ccTerminals.pushBack(tC);
            ccIsTerminal[tC] = true;
        }
 
        // solve compact copy
        EdgeWeightedGraphCopy<T>* ccSolution = nullptr;
        T cost = mst.call(ccGraph, ccTerminals, ccIsTerminal, ccSolution);
        cost += costEdgesAlreadyInserted();
 
        // get reduced and original solution from compact copy solution
        EdgeWeightedGraphCopy<T> reducedSolution;
        reducedSolution.createEmpty(m_copyGraph);
        for (node v : m_copyGraph.nodes) {
            if (ccSolution->copy(nCopy[v]) != nullptr) { // is in solution
                reducedSolution.newNode(v);
            }
        }
        for (edge e : m_copyGraph.edges) {
            if (ccSolution->copy(eCopy[e]) != nullptr) { // is in solution
                reducedSolution.newEdge(e, m_copyGraph.weight(e));
            }
        }
        delete ccSolution;
 
        computeOriginalSolution(reducedSolution, *finalSteinerTree);
        return cost;
    }
 
    inline const EdgeWeightedGraph<T>& getReducedGraph() const { return m_copyGraph; }
 
    inline const List<node>& getReducedTerminals() const { return m_copyTerminals; }
 
    inline void shuffleReducedTerminals() { m_copyTerminals.permute(); }
 
    inline const NodeArray<bool>& getReducedIsTerminal() const { return m_copyIsTerminal; }
 
 
    inline T costEdgesAlreadyInserted() const { return m_costAlreadyInserted; }
 
    void computeOriginalSolution(const EdgeWeightedGraphCopy<T>& reducedGraphSolution,
            EdgeWeightedGraphCopy<T>& correspondingOriginalSolution);
 
 
 
    bool reduceTrivial() {
        return repeat([this]() {
            bool changed = false;
            changed |= degree2Test();
            changed |= makeSimple();
            changed |= deleteLeaves();
            return changed;
        });
    }
 
    bool reduceFast() {
        int k = 5; // for PTmTest
        // comment wrt. Apple Clang 10: making k const, results in compiler error while binding it in lambda
        // comment wrt. MSVC 19: not binding the const k would result in compiler error
 
        bool changed = deleteComponentsWithoutTerminals();
        bool triviallyChanged = false;
        changed |= repeat([this, &triviallyChanged, k]() {
            bool innerChanged = false;
            triviallyChanged = reduceTrivial();
            // graph guaranteed to be simple and connected
 
            if (nearestVertexTest()) {
                makeSimple();
                innerChanged = true;
            }
 
            // precond: connected
            if (terminalDistanceTest()) {
                // can occur: disconnected
                deleteComponentsWithoutTerminals();
                innerChanged = true;
            }
 
            // precond: simple, connected
            innerChanged |= NTDkTest(10, k);
            // can occur: parallel edges
 
            // precond: connected
            innerChanged |= shortLinksTest();
            // can occur: parallel edges, self-loops
 
            // precond: connected
            innerChanged |= lowerBoundBasedTest();
 
            // is not thaaat good but helps a little:
            innerChanged |= PTmTest(k);
            // can occur: parallel edges
 
            return innerChanged;
        });
        return changed | triviallyChanged;
    }
 
    bool reduceFastAndDualAscent() {
        return repeat([this] {
            bool changed = reduceFast();
            changed |= dualAscentBasedTest();
            return changed;
        });
    }
 
 
 
    bool deleteLeaves();
 
    bool makeSimple();
 
    bool deleteComponentsWithoutTerminals();
 
    bool leastCostTest();
 
    bool degree2Test();
 
    bool PTmTest(const int k = 3);
 
    bool terminalDistanceTest();
 
    bool longEdgesTest();
 
    bool NTDkTest(const int maxTestedDegree = 5, const int k = 3);
 
    bool nearestVertexTest();
 
    bool shortLinksTest();
 
    bool lowerBoundBasedTest(T upperBound);
 
    inline bool lowerBoundBasedTest() {
        return lowerBoundBasedTest(computeMinSteinerTreeUpperBound());
    }
 
    bool dualAscentBasedTest(int repetitions, T upperBound);
 
    inline bool dualAscentBasedTest(int repetitions = 1) {
        return dualAscentBasedTest(repetitions, computeMinSteinerTreeUpperBound());
    }
 
    bool reachabilityTest(int maxDegreeTest = 0, const int k = 3);
 
    bool cutReachabilityTest();
 
 
    inline void setCostUpperBoundAlgorithm(MinSteinerTreeModule<T>* pMinSteinerTreeModule) {
        m_costUpperBoundAlgorithm.reset(pMinSteinerTreeModule);
    }
 
 
    static bool repeat(std::function<bool()> f) {
        bool changed = false;
        while (f()) {
            changed = true;
        }
        return changed;
    }
 
protected:
    template<typename TWhat, typename TWhatArray>
    void addNew(TWhat x, const std::vector<node>& replacedNodes,
            const std::vector<edge>& replacedEdges, bool deleteReplacedElements,
            TWhatArray& whatSonsListIndex);
 
    inline void addNewNode(node v, const std::vector<node>& replacedNodes,
            const std::vector<edge>& replacedEdges, bool deleteReplacedElements) {
        addNew(v, replacedNodes, replacedEdges, deleteReplacedElements, m_nodeSonsListIndex);
    }
 
    inline void addNewEdge(edge e, const std::vector<node>& replacedNodes,
            const std::vector<edge>& replacedEdges, bool deleteReplacedElements) {
        addNew(e, replacedNodes, replacedEdges, deleteReplacedElements, m_edgeSonsListIndex);
    }
 
    bool addEdgesToSolution(const List<edge>& edgesToBeAddedInSolution);
 
    void recomputeTerminalsList();
 
    void computeShortestPathMatrix(NodeArray<NodeArray<T>>& shortestPath) const;
 
    void floydWarshall(NodeArray<NodeArray<T>>& shortestPath) const;
 
    inline T computeMinSteinerTreeUpperBound(EdgeWeightedGraphCopy<T>*& finalSteinerTree) const {
        finalSteinerTree = nullptr;
        return m_costUpperBoundAlgorithm->call(m_copyGraph, m_copyTerminals, m_copyIsTerminal,
                finalSteinerTree);
    }
 
    // for convenience:
    inline T computeMinSteinerTreeUpperBound() const {
        EdgeWeightedGraphCopy<T>* finalSteinerTree;
        T treeCostUpperBound = computeMinSteinerTreeUpperBound(finalSteinerTree);
        delete finalSteinerTree;
        return treeCostUpperBound;
    }
 
    void addToSolution(const int listIndex, Array<bool, int>& isInSolution) const;
 
    bool deleteNodesAboveUpperBound(const NodeArray<T>& lowerBoundWithNode, const T upperBound);
    bool deleteEdgesAboveUpperBound(const EdgeArray<T>& lowerBoundWithEdge, const T upperBound);
 
    void deleteSteinerDegreeTwoNode(node v, const EdgeWeightedGraphCopy<T>& tprime,
            const steiner_tree::HeavyPathDecomposition<T>& tprimeHPD,
            const NodeArray<List<std::pair<node, T>>>& closestTerminals);
 
    void findClosestNonTerminals(node source, List<node>& reachedNodes, NodeArray<T>& distance,
            T maxDistance, int expandedEdges) const;
 
    T computeBottleneckDistance(node x, node y, const EdgeWeightedGraphCopy<T>& tprime,
            const steiner_tree::HeavyPathDecomposition<T>& tprimeHPD,
            const NodeArray<List<std::pair<node, T>>>& closestTerminals) const;
 
    void computeClosestKTerminals(const int k,
            NodeArray<List<std::pair<node, T>>>& closestTerminals) const;
 
    void computeRadiusOfTerminals(NodeArray<T>& terminalRadius) const;
 
    T computeRadiusSum() const;
 
    template<typename LAMBDA>
    void computeOptimalTerminals(node v, LAMBDA dist, node& optimalTerminal1,
            node& optimalTerminal2, NodeArray<T>& distance) const;
 
    void markSuccessors(node currentNode, const Voronoi<T>& voronoiRegions,
            NodeArray<bool>& isSuccessorOfMinCostEdge) const;
 
    void findTwoMinimumCostEdges(node v, edge& first, edge& second) const;
};
 
template<typename T>
SteinerTreePreprocessing<T>::SteinerTreePreprocessing(const EdgeWeightedGraph<T>& wg,
        const List<node>& terminals, const NodeArray<bool>& isTerminal)
    : m_origGraph(wg), m_origTerminals(terminals), m_origIsTerminal(isTerminal), m_eps(1e-6) {
    OGDF_ASSERT(!m_origGraph.empty());
 
    // make the initial graph copy
    m_copyGraph.clear();
    NodeArray<node> nCopy(m_origGraph);
    EdgeArray<edge> eCopy(m_origGraph);
 
    for (node v : m_origGraph.nodes) {
        nCopy[v] = m_copyGraph.newNode();
    }
    for (edge e : m_origGraph.edges) {
        eCopy[e] = m_copyGraph.newEdge(nCopy[e->source()], nCopy[e->target()], m_origGraph.weight(e));
    }
 
    // create the terminals and isTerminal arrays for the copyGraph
    m_copyTerminals.clear();
    m_copyIsTerminal.init(m_copyGraph, false);
    for (node v : m_origGraph.nodes) {
        if (m_origIsTerminal(v)) {
            const node vC = nCopy[v];
            m_copyTerminals.pushBack(vC);
            m_copyIsTerminal[vC] = true;
        }
    }
    m_costAlreadyInserted = 0;
 
    // map every node and edge to a negative number for m_(node/edge)_m_sonsListIndex
    m_nodeSonsListIndex.init(m_copyGraph);
    m_edgeSonsListIndex.init(m_copyGraph);
    int nextIndex = 1;
    for (node v : m_origGraph.nodes) {
        m_nodeSonsListIndex[nCopy[v]] = -(nextIndex++);
    }
    for (edge e : m_origGraph.edges) {
        m_edgeSonsListIndex[eCopy[e]] = -(nextIndex++);
    }
 
    // set the default approximation algorithm for computing the upper bound cost of the solution
    m_costUpperBoundAlgorithm.reset(new MinSteinerTreeTakahashi<T>);
}
 
template<typename T>
template<typename TWhat, typename TWhatArray>
void SteinerTreePreprocessing<T>::addNew(TWhat x, const std::vector<node>& replacedNodes,
        const std::vector<edge>& replacedEdges, bool deleteReplacedElements,
        TWhatArray& whatSonsListIndex) {
    std::vector<int> sonsIndexList;
    for (node replacedNode : replacedNodes) {
        sonsIndexList.push_back(m_nodeSonsListIndex[replacedNode]);
    }
    for (edge replacedEdge : replacedEdges) {
        sonsIndexList.push_back(m_edgeSonsListIndex[replacedEdge]);
    }
 
    m_sonsList.emplace_back(sonsIndexList);
    whatSonsListIndex[x] = (int)m_sonsList.size() - 1;
 
    if (deleteReplacedElements) {
        for (edge e : replacedEdges) {
            m_copyGraph.delEdge(e);
        }
        for (node v : replacedNodes) {
            m_copyGraph.delNode(v);
        }
    }
}
 
template<typename T>
void SteinerTreePreprocessing<T>::addToSolution(const int listIndex,
        Array<bool, int>& isInSolution) const {
    if (listIndex < 0) { // is starting node or edge
        isInSolution[listIndex] = true;
        return;
    }
    // is further added node or edge
    for (int son : m_sonsList[listIndex]) {
        addToSolution(son, isInSolution);
    }
}
 
template<typename T>
void SteinerTreePreprocessing<T>::computeOriginalSolution(
        const EdgeWeightedGraphCopy<T>& reducedGraphSolution,
        EdgeWeightedGraphCopy<T>& correspondingOriginalSolution) {
    correspondingOriginalSolution.createEmpty(m_origGraph); // note that it is not cleared!
 
    Array<bool, int> isInSolution(-(m_origGraph.numberOfNodes() + m_origGraph.numberOfEdges()), -1,
            false);
 
    // make the indices of original nodes/edge true in isInSolution
    for (node v : reducedGraphSolution.nodes) {
        addToSolution(m_nodeSonsListIndex[reducedGraphSolution.original(v)], isInSolution);
    }
    for (edge e : reducedGraphSolution.edges) {
        addToSolution(m_edgeSonsListIndex[reducedGraphSolution.original(e)], isInSolution);
    }
 
    // insert nodes and edges
    int nextIndex = 1;
    for (node v : m_origGraph.nodes) {
        if (isInSolution[-(nextIndex++)]) {
            correspondingOriginalSolution.newNode(v);
        }
    }
    for (edge e : m_origGraph.edges) {
        if (isInSolution[-(nextIndex++)]) {
            correspondingOriginalSolution.newEdge(e, m_origGraph.weight(e));
        }
    }
}
 
template<typename T>
void SteinerTreePreprocessing<T>::deleteSteinerDegreeTwoNode(node v,
        const EdgeWeightedGraphCopy<T>& tprime,
        const steiner_tree::HeavyPathDecomposition<T>& tprimeHPD,
        const NodeArray<List<std::pair<node, T>>>& closestTerminals) {
    struct NewEdgeData {
        edge e1; // new edge replaces this...
        edge e2; // ...and this
        edge already; // but is it already there?
        T weight;
    };
 
    std::forward_list<NewEdgeData> newEdges;
    for (adjEntry adj1 : v->adjEntries) {
        const edge e1 = adj1->theEdge();
        const node adjacentNode1 = adj1->twinNode();
 
        for (adjEntry adj2 = adj1->succ(); adj2; adj2 = adj2->succ()) {
            const edge e2 = adj2->theEdge();
            const node adjacentNode2 = adj2->twinNode();
 
            T edgeWeight = m_copyGraph.weight(e1) + m_copyGraph.weight(e2);
 
            const edge f = m_copyGraph.searchEdge(adjacentNode1, adjacentNode2);
            if (f && m_copyGraph.weight(f) <= edgeWeight) {
                continue; // check whether there is already a lower cost edge connecting the two adjacent nodes
            }
 
            T bottleneckDistance = computeBottleneckDistance(adjacentNode1, adjacentNode2, tprime,
                    tprimeHPD, closestTerminals);
            if (m_eps.greater(edgeWeight, bottleneckDistance)) {
                continue; // the PTm test
            }
 
            newEdges.emplace_front(NewEdgeData {e1, e2, f, edgeWeight});
        }
    }
 
    for (const auto& newEdge : newEdges) {
        // delete the old edge (do not generate parallel edges)
        edge newEdgeInGraph;
        if (newEdge.already) {
            OGDF_ASSERT(m_copyGraph.weight(newEdge.already) > newEdge.weight);
            m_copyGraph.setWeight(newEdge.already, newEdge.weight);
            newEdgeInGraph = newEdge.already;
        } else {
            newEdgeInGraph = m_copyGraph.newEdge(newEdge.e1->opposite(v), newEdge.e2->opposite(v),
                    newEdge.weight);
        }
        addNewEdge(newEdgeInGraph, {v}, {newEdge.e1, newEdge.e2}, false);
    }
 
    m_copyGraph.delNode(v);
}
 
template<typename T>
void SteinerTreePreprocessing<T>::recomputeTerminalsList() {
    m_copyTerminals.clear();
    for (node v : m_copyGraph.nodes) {
        if (m_copyIsTerminal[v]) {
            m_copyTerminals.pushBack(v);
        }
    }
}
 
template<typename T>
T SteinerTreePreprocessing<T>::computeBottleneckDistance(node x, node y,
        const EdgeWeightedGraphCopy<T>& tprime,
        const steiner_tree::HeavyPathDecomposition<T>& tprimeHPD,
        const NodeArray<List<std::pair<node, T>>>& closestTerminals) const {
    T bottleneckDistance = std::numeric_limits<T>::max();
 
    for (auto& xCloseTerminalDistancePair : closestTerminals[x]) {
        for (auto& yCloseTerminalDistancePair : closestTerminals[y]) {
            T possibleBottleneckDistance =
                    xCloseTerminalDistancePair.second + yCloseTerminalDistancePair.second;
 
            node xTprimeCopy = tprime.copy(xCloseTerminalDistancePair.first);
            node yTprimeCopy = tprime.copy(yCloseTerminalDistancePair.first);
            possibleBottleneckDistance +=
                    tprimeHPD.getBottleneckSteinerDistance(xTprimeCopy, yTprimeCopy);
 
            Math::updateMin(bottleneckDistance, possibleBottleneckDistance);
        }
    }
 
    return bottleneckDistance;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::deleteLeaves() {
    // exceptional case: only one terminal
    auto deleteAll = [this]() {
        if (m_copyGraph.numberOfNodes() > 1) {
            const node w = m_copyTerminals.front();
            // just remove all other nodes
            for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
                nextV = v->succ();
                if (v != w) {
                    m_copyGraph.delNode(v);
                }
            }
            return true;
        }
        return false;
    };
    if (m_copyTerminals.size() == 1) {
        return deleteAll();
    }
    // general case: at least 2 terminals
    BoundedQueue<node> eraseQueue(m_copyGraph.numberOfNodes());
 
    for (node v : m_copyGraph.nodes) {
        if (v->degree() == 1) {
            eraseQueue.append(v);
        }
    }
 
    if (eraseQueue.empty()) {
        return false;
    }
 
    for (; !eraseQueue.empty(); eraseQueue.pop()) {
        node v = eraseQueue.top();
        if (v->degree() == 0) {
            continue;
        }
        OGDF_ASSERT(v->degree() == 1);
        const node w = v->firstAdj()->twinNode();
        if (m_copyIsTerminal[v]) { // v is a terminal
            // add edge to solution and contract v into w
            edge e = v->firstAdj()->theEdge();
            if (!m_copyIsTerminal[w]) {
                m_copyIsTerminal[w] = true;
                m_copyTerminals.pushBack(w);
            }
            m_copyTerminals.del(m_copyTerminals.search(v));
            m_costAlreadyInserted += m_copyGraph.weight(e);
            int cur = m_nodeSonsListIndex[w];
            if (cur < 0) { // w is an original (copied) node
                m_sonsList.emplace_back(
                        std::vector<int> {cur, m_nodeSonsListIndex[v], m_edgeSonsListIndex[e]});
                m_nodeSonsListIndex[w] = (int)m_sonsList.size() - 1;
            } else { // w contains already sons
                m_sonsList[cur].push_back(m_nodeSonsListIndex[v]);
                m_sonsList[cur].push_back(m_edgeSonsListIndex[e]);
            }
        } else { // v is not a terminal
            if (w->degree() == 2) {
                eraseQueue.append(w);
            }
        }
        m_copyGraph.delNode(v);
        if (m_copyTerminals.size() == 1) {
            deleteAll();
            return true;
        }
    }
    return true;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::makeSimple() {
    bool changed = false;
    NodeArray<edge> minCostEdge(m_copyGraph, nullptr);
    for (node v : m_copyGraph.nodes) {
        for (adjEntry adj = v->firstAdj(), nextAdj; adj; adj = nextAdj) {
            nextAdj = adj->succ();
 
            edge e = adj->theEdge();
            node adjNode = adj->twinNode();
            if (adjNode == v) { // found a self-loop
                if (nextAdj == adj->twin()) {
                    nextAdj = nextAdj->succ();
                }
                m_copyGraph.delEdge(e);
                changed = true;
            } else {
                if (minCostEdge[adjNode] == nullptr
                        || m_copyGraph.weight(minCostEdge[adjNode]) > m_copyGraph.weight(e)) {
                    if (minCostEdge[adjNode] != nullptr) {
                        m_copyGraph.delEdge(minCostEdge[adjNode]);
                        changed = true;
                    }
                    minCostEdge[adjNode] = e;
                } else {
                    m_copyGraph.delEdge(e);
                    changed = true;
                }
            }
        }
 
        for (adjEntry adj : v->adjEntries) {
            minCostEdge[adj->twinNode()] = nullptr;
        }
    }
    return changed;
}
 
template<typename T>
void SteinerTreePreprocessing<T>::floydWarshall(NodeArray<NodeArray<T>>& shortestPath) const {
    for (node v1 : m_copyGraph.nodes) {
        for (adjEntry adj : v1->adjEntries) {
            node v2 = adj->twinNode();
            shortestPath[v1][v2] = shortestPath[v2][v1] =
                    min(shortestPath[v1][v2], m_copyGraph.weight(adj->theEdge()));
        }
    }
 
    for (node pivot : m_copyGraph.nodes) {
        for (node v1 : m_copyGraph.nodes) {
            for (node v2 : m_copyGraph.nodes) {
                if (shortestPath[v1][pivot] == std::numeric_limits<T>::max()
                        || shortestPath[pivot][v2] == std::numeric_limits<T>::max()) {
                    continue;
                }
 
                Math::updateMin(shortestPath[v1][v2],
                        shortestPath[v1][pivot] + shortestPath[pivot][v2]);
            }
        }
    }
}
 
template<typename T>
inline void SteinerTreePreprocessing<T>::computeShortestPathMatrix(
        NodeArray<NodeArray<T>>& shortestPath) const {
    shortestPath.init(m_copyGraph);
    for (node v : m_copyGraph.nodes) {
        shortestPath[v].init(m_copyGraph, std::numeric_limits<T>::max());
    }
 
    floydWarshall(shortestPath);
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::leastCostTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    bool changed = false;
    NodeArray<NodeArray<T>> shortestPath;
    computeShortestPathMatrix(shortestPath);
 
    for (node v : m_copyGraph.nodes) {
        for (adjEntry adj = v->firstAdj(), nextAdj; adj; adj = nextAdj) {
            nextAdj = adj->succ();
 
            edge e = adj->theEdge();
            node adjNode = adj->twinNode();
            if (adjNode != v && shortestPath[v][adjNode] < m_copyGraph.weight(e)) {
                m_copyGraph.delEdge(e);
                changed = true;
            }
        }
    }
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::degree2Test() {
    OGDF_ASSERT(!m_copyGraph.empty());
    bool changed = false;
    for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
        nextV = v->succ();
 
        if (m_copyIsTerminal[v] || v->degree() != 2) {
            continue;
        }
 
        // get left and right adjacent nodes
        edge eLeft = v->firstAdj()->theEdge();
        edge eRight = v->lastAdj()->theEdge();
 
        node vLeft = v->firstAdj()->twinNode();
        node vRight = v->lastAdj()->twinNode();
        if (vLeft != vRight) {
            T weight = m_copyGraph.weight(eLeft) + m_copyGraph.weight(eRight);
            edge newEdge = m_copyGraph.newEdge(vLeft, vRight, weight);
            addNewEdge(newEdge, {v}, {eLeft, eRight}, true);
            changed = true;
        } else { // v is leaf with parallel edges or self-loop component
            m_copyGraph.delNode(v);
        }
    }
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::deleteComponentsWithoutTerminals() {
    NodeArray<int> hisConnectedComponent(m_copyGraph, -1);
    bool changed = connectedComponents(m_copyGraph, hisConnectedComponent) > 1;
    if (changed) {
        int componentWithTerminals = -1;
        for (node v : m_copyTerminals) {
            if (componentWithTerminals != -1 && hisConnectedComponent[v] != componentWithTerminals) {
                std::cerr << "terminals in different connected components!\n";
                OGDF_ASSERT(false);
            }
            componentWithTerminals = hisConnectedComponent[v];
        }
 
        for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
            nextV = v->succ();
            if (hisConnectedComponent[v] != componentWithTerminals) {
                m_copyGraph.delNode(v);
            }
        }
    }
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::terminalDistanceTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    OGDF_ASSERT(isConnected(m_copyGraph));
    bool changed = false;
 
    EdgeWeightedGraphCopy<T> tprime;
    steiner_tree::constructTerminalSpanningTreeUsingVoronoiRegions(tprime, m_copyGraph,
            m_copyTerminals);
    T maxBottleneck(0);
    for (edge e : tprime.edges) {
        Math::updateMax(maxBottleneck, tprime.weight(e));
    }
 
    for (edge e = m_copyGraph.firstEdge(), nextE; e; e = nextE) {
        nextE = e->succ();
 
        if (m_eps.greater(m_copyGraph.weight(e), maxBottleneck)) {
            m_copyGraph.delEdge(e);
            changed = true;
        }
    }
 
    return changed;
}
 
template<typename T>
void SteinerTreePreprocessing<T>::findClosestNonTerminals(node source, List<node>& reachedNodes,
        NodeArray<T>& distance, T maxDistance, int expandedEdges) const {
    PrioritizedMapQueue<node, T> queue(m_copyGraph);
 
    // initialization
    distance[source] = 0;
    queue.push(source, distance[source]);
 
    while (!queue.empty()) {
        node currentNode = queue.topElement();
        queue.pop();
 
        reachedNodes.pushBack(currentNode);
 
        for (adjEntry adj : currentNode->adjEntries) {
            edge e = adj->theEdge();
            if (expandedEdges <= 0) {
                break;
            }
            --expandedEdges;
 
            node adjacentNode = e->opposite(currentNode);
            T possibleDistance = distance[currentNode] + m_copyGraph.weight(e);
 
            if (m_eps.geq(possibleDistance, maxDistance) || m_copyIsTerminal[adjacentNode]) {
                continue;
            }
 
            if (possibleDistance < distance[adjacentNode]) {
                distance[adjacentNode] = possibleDistance;
                if (queue.contains(adjacentNode)) { // is already in the queue
                    queue.decrease(adjacentNode, possibleDistance);
                } else {
                    queue.push(adjacentNode, distance[adjacentNode]);
                }
            }
        }
    }
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::longEdgesTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    bool changed = false;
    NodeArray<T> xDistance(m_copyGraph, std::numeric_limits<T>::max()),
            yDistance(m_copyGraph, std::numeric_limits<T>::max());
 
    for (edge e = m_copyGraph.firstEdge(), nextE; e; e = nextE) {
        nextE = e->succ();
        List<node> xReachedNodes, yReachedNodes;
 
        findClosestNonTerminals(e->source(), xReachedNodes, xDistance, m_copyGraph.weight(e), 200);
        findClosestNonTerminals(e->target(), yReachedNodes, yDistance, m_copyGraph.weight(e), 200);
 
        for (node commonNode : xReachedNodes) {
            if (yDistance[commonNode] == std::numeric_limits<T>::max()) { // is not common
                continue;
            }
            if (m_eps.less(xDistance[commonNode] + yDistance[commonNode], m_copyGraph.weight(e))) {
                m_copyGraph.delEdge(e);
                changed = true;
                break;
            }
        }
 
        for (node reachedNode : xReachedNodes) {
            xDistance[reachedNode] = std::numeric_limits<T>::max();
        }
        for (node reachedNode : yReachedNodes) {
            yDistance[reachedNode] = std::numeric_limits<T>::max();
        }
    }
    return changed;
}
 
template<typename T>
void SteinerTreePreprocessing<T>::computeClosestKTerminals(const int k,
        NodeArray<List<std::pair<node, T>>>& closestTerminals) const {
    using NodePairQueue = PrioritizedQueue<NodePair, T>;
 
    closestTerminals.init(m_copyGraph);
    NodePairQueue queue;
    std::unordered_map<NodePair, typename NodePairQueue::Handle,
            steiner_tree::UnorderedNodePairHasher, steiner_tree::UnorderedNodePairEquality>
            qpos;
 
    // initialization
    for (node v : m_copyTerminals) {
        closestTerminals[v].pushBack(std::make_pair(v, 0));
        qpos[NodePair(v, v)] = queue.push(NodePair(v, v), closestTerminals[v].front().second);
    }
 
    auto getCurrentDist = [&closestTerminals](const node currentNode, const node sourceTerminal) {
        for (std::pair<node, T> currentPair : closestTerminals[currentNode]) {
            if (currentPair.first == sourceTerminal) {
                return currentPair.second;
            }
        }
        return static_cast<T>(-1);
    };
 
    auto setNewDist = [&closestTerminals, k](const node currentNode, const node sourceTerminal,
                              const T newDist) {
        List<std::pair<node, T>>& currentList = closestTerminals[currentNode];
 
        // delete the old distance
        for (ListIterator<std::pair<node, T>> it = currentList.begin(); it.valid(); ++it) {
            if ((*it).first == sourceTerminal) {
                currentList.del(it);
                break;
            }
        }
 
        if (currentList.size() == k) { // the list is full
            currentList.popBack(); // delete the largest cost element
        }
 
        // add the new distance such that the list remains sorted
        if (currentList.empty() || (*currentList.begin()).second >= newDist) { // if the list is empty
            currentList.pushFront(std::make_pair(sourceTerminal, newDist));
            return;
        }
 
        ListIterator<std::pair<node, T>> it = closestTerminals[currentNode].begin();
        while (it.succ() != closestTerminals[currentNode].end() && (*it.succ()).second < newDist) {
            ++it;
        }
        closestTerminals[currentNode].insertAfter(std::make_pair(sourceTerminal, newDist), it);
    };
 
    while (!queue.empty()) {
        NodePair minDistPair = queue.topElement();
        queue.pop();
        node currentNode = minDistPair.source;
        node sourceTerminal = minDistPair.target;
 
        T currentDist = getCurrentDist(currentNode, sourceTerminal);
        if (currentDist == -1) { // source terminal not found
            continue; // check if the current path needs to be expanded
        }
 
        for (adjEntry adj : currentNode->adjEntries) {
            edge e = adj->theEdge();
            node adjacentNode = e->opposite(currentNode);
 
            if (m_copyIsTerminal[adjacentNode]) {
                continue;
            }
 
            T possibleNewDistance = currentDist + m_copyGraph.weight(e);
 
            // try to insert the new path from sourceTerminal to adjacentNode
            T currentDistToAdjacentNode = getCurrentDist(adjacentNode, sourceTerminal);
            if (currentDistToAdjacentNode
                    != -1) { // there is already one path from sourceTerminal to adjNode
                if (possibleNewDistance < currentDistToAdjacentNode) {
                    queue.decrease(qpos[NodePair(adjacentNode, sourceTerminal)], possibleNewDistance);
                    setNewDist(adjacentNode, sourceTerminal, possibleNewDistance);
                }
            } else {
                if (closestTerminals[adjacentNode].size() < k
                        || closestTerminals[adjacentNode].back().second > possibleNewDistance) {
                    qpos[NodePair(adjacentNode, sourceTerminal)] =
                            queue.push(NodePair(adjacentNode, sourceTerminal), possibleNewDistance);
                    setNewDist(adjacentNode, sourceTerminal, possibleNewDistance);
                }
            }
        }
    }
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::PTmTest(const int k) {
    OGDF_ASSERT(!m_copyGraph.empty());
    OGDF_ASSERT(isConnected(m_copyGraph));
    bool changed = false;
 
    EdgeWeightedGraphCopy<T> tprime;
    steiner_tree::constructTerminalSpanningTreeUsingVoronoiRegions(tprime, m_copyGraph,
            m_copyTerminals);
 
    NodeArray<List<std::pair<node, T>>> closestTerminals;
    computeClosestKTerminals(k, closestTerminals);
 
    steiner_tree::HeavyPathDecomposition<T> tprimeHPD(tprime);
 
    for (edge e = m_copyGraph.firstEdge(), nextE; e; e = nextE) {
        nextE = e->succ();
 
        T bottleneckDistance = computeBottleneckDistance(e->source(), e->target(), tprime,
                tprimeHPD, closestTerminals);
 
        if (m_eps.greater(m_copyGraph.weight(e), bottleneckDistance)) {
            m_copyGraph.delEdge(e);
            changed = true;
        }
    }
 
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::NTDkTest(const int maxTestedDegree, const int k) {
    OGDF_ASSERT(!m_copyGraph.empty());
    if (m_copyTerminals.size() <= 2) {
        return false;
    }
 
    bool changed = false;
    OGDF_ASSERT(isSimpleUndirected(m_copyGraph));
    OGDF_ASSERT(isConnected(m_copyGraph));
 
    EdgeWeightedGraphCopy<T> tprime;
    steiner_tree::constructTerminalSpanningTreeUsingVoronoiRegions(tprime, m_copyGraph,
            m_copyTerminals);
 
    NodeArray<List<std::pair<node, T>>> closestTerminals;
    computeClosestKTerminals(k, closestTerminals);
 
    steiner_tree::HeavyPathDecomposition<T> tprimeHPD(tprime);
 
    for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
        nextV = v->succ();
 
        if (m_copyIsTerminal[v]) {
            continue;
        }
        if (v->degree() <= 2 || v->degree() > maxTestedDegree) {
            continue;
        }
 
        // collect neighbors
        List<adjEntry> outgoingAdjs;
        for (adjEntry adj : v->adjEntries) {
            outgoingAdjs.pushBack(adj);
        }
        SubsetEnumerator<adjEntry> neighborSubset(outgoingAdjs);
 
        bool deleteNode = true;
        for (neighborSubset.begin(3, v->degree()); neighborSubset.valid() && deleteNode;
                neighborSubset.next()) {
            Graph auxGraph;
            std::unordered_map<node, node> initNodeToAuxGraph;
            std::unordered_map<node, node> auxGraphToInitNode;
 
            T sumToSelectedAdjacentNodes = 0;
 
            for (int i = 0; i < neighborSubset.size(); ++i) {
                const adjEntry adj = neighborSubset[i];
                const node adjacentNode = adj->twinNode();
                sumToSelectedAdjacentNodes += m_copyGraph.weight(adj->theEdge());
 
                OGDF_ASSERT(initNodeToAuxGraph.find(adjacentNode) == initNodeToAuxGraph.end());
 
                node newAuxGraphNode = auxGraph.newNode();
                initNodeToAuxGraph[adjacentNode] = newAuxGraphNode;
                auxGraphToInitNode[newAuxGraphNode] = adjacentNode;
            }
 
            EdgeArray<T> weight(auxGraph, 0);
            for (node auxGraphNode1 : auxGraph.nodes) {
                for (node auxGraphNode2 = auxGraphNode1->succ(); auxGraphNode2;
                        auxGraphNode2 = auxGraphNode2->succ()) {
                    edge e = auxGraph.newEdge(auxGraphNode1, auxGraphNode2);
                    weight[e] = computeBottleneckDistance(auxGraphToInitNode[auxGraphNode1],
                            auxGraphToInitNode[auxGraphNode2], tprime, tprimeHPD, closestTerminals);
                }
            }
 
            // the auxGraph is now created; run MST on it
            EdgeArray<bool> isInTree(auxGraph, false);
            T mstCost = computeMinST(auxGraph, weight, isInTree);
 
            if (sumToSelectedAdjacentNodes < mstCost) {
                deleteNode = false;
            }
        }
 
        if (deleteNode) {
            deleteSteinerDegreeTwoNode(v, tprime, tprimeHPD, closestTerminals);
            changed = true;
        }
    }
 
    return changed;
}
 
template<typename T>
void SteinerTreePreprocessing<T>::markSuccessors(node currentNode, const Voronoi<T>& voronoiRegions,
        NodeArray<bool>& isSuccessorOfMinCostEdge) const {
    isSuccessorOfMinCostEdge[currentNode] = true;
 
    OGDF_ASSERT(voronoiRegions.seed(currentNode) != currentNode);
 
    // recurse for every successor
    for (adjEntry adj : currentNode->adjEntries) {
        edge e = adj->theEdge();
        node adjacentNode = e->opposite(currentNode);
 
        if (voronoiRegions.predecessor(adjacentNode) == currentNode) {
            markSuccessors(adjacentNode, voronoiRegions, isSuccessorOfMinCostEdge);
        }
    }
}
 
template<typename T>
void SteinerTreePreprocessing<T>::findTwoMinimumCostEdges(node v, edge& first, edge& second) const {
    /* This is a simple problem, however, there is a weird case that can occur
     * in nearestVertexTest(): Imagine a triangle of three terminals where the three edges
     * have all equal costs. It can happen that each terminal chooses its first edge to
     * be unique, so in the end we add all three edges of the triangle except only two of it.
     * We tackle this problem at *this* stage by choosing the edge with smallest index
     * in case of a tie in the costs. It is sufficient to do that for the first only
     * because this is the edge that will be put into the solution. */
    for (adjEntry adj : v->adjEntries) {
        edge e = adj->theEdge();
        if (first == nullptr // not set or
                || m_eps.less(m_copyGraph.weight(e), m_copyGraph.weight(first)) // smaller cost or
                || (m_eps.equal(m_copyGraph.weight(e), m_copyGraph.weight(first)) // cost tie but...
                        && e->index() < first->index())) { // cost tie but smaller index
            second = first;
            first = e;
        } else {
            if (second == nullptr || m_eps.less(m_copyGraph.weight(e), m_copyGraph.weight(second))) {
                second = e;
            }
        }
    }
    OGDF_ASSERT(first != second);
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::addEdgesToSolution(const List<edge>& edgesToBeAddedInSolution) {
    if (edgesToBeAddedInSolution.empty()) {
        return false;
    }
    for (edge e : edgesToBeAddedInSolution) {
        node x = e->source(), y = e->target();
        m_sonsList.emplace_back(std::vector<int> {
                m_nodeSonsListIndex[x], m_nodeSonsListIndex[y], m_edgeSonsListIndex[e]});
        m_costAlreadyInserted += m_copyGraph.weight(e);
        node newNode = m_copyGraph.contract(e);
        m_nodeSonsListIndex[newNode] = (int)m_sonsList.size() - 1;
        m_copyIsTerminal[newNode] = true;
    }
 
    recomputeTerminalsList();
    return true;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::nearestVertexTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    OGDF_ASSERT(isLoopFree(m_copyGraph));
    OGDF_ASSERT(isConnected(m_copyGraph));
 
    Voronoi<T> voronoiRegions(m_copyGraph, m_copyGraph.edgeWeights(), m_copyTerminals);
 
    NodeArray<edge> minCostIncidentEdge1(m_copyGraph, nullptr);
    NodeArray<edge> minCostIncidentEdge2(m_copyGraph, nullptr);
 
    // find the first and second minimum-cost edges incident to terminals
    for (node terminal : m_copyTerminals) {
        if (terminal->degree() >= 2) {
            findTwoMinimumCostEdges(terminal, minCostIncidentEdge1[terminal],
                    minCostIncidentEdge2[terminal]);
        }
    }
 
    // for each Voronoi region, mark successors (recursively) of the minimum-cost edge
    NodeArray<bool> isSuccessorOfMinCostEdge(m_copyGraph, false);
    for (node terminal : m_copyTerminals) {
        if (terminal->degree() >= 2) {
            node closestNode = minCostIncidentEdge1[terminal]->opposite(terminal);
 
            if (voronoiRegions.seed(closestNode) == terminal) {
                markSuccessors(closestNode, voronoiRegions, isSuccessorOfMinCostEdge);
            }
        }
    }
 
    // compute for every terminal the distance to the closest terminal
    NodeArray<T> distanceToClosestTerminal(m_copyGraph, std::numeric_limits<T>::max());
    for (edge e : m_copyGraph.edges) {
        node x = e->source(), y = e->target();
        node seedX = voronoiRegions.seed(x), seedY = voronoiRegions.seed(y);
        if (seedX != seedY) {
            // update distanceToClosestTerminal for seed(x)
            T distanceThroughE =
                    voronoiRegions.distance(x) + m_copyGraph.weight(e) + voronoiRegions.distance(y);
 
            if (isSuccessorOfMinCostEdge[x]) {
                Math::updateMin(distanceToClosestTerminal[seedX], distanceThroughE);
            }
            if (isSuccessorOfMinCostEdge[y]) {
                Math::updateMin(distanceToClosestTerminal[seedY], distanceThroughE);
            }
        }
    }
 
    // see what edges can be added in solution (Observation 3.2)
    List<edge> edgesToBeAddedInSolution;
    EdgeArray<bool> willBeAddedInSolution(m_copyGraph, false);
    for (node terminal : m_copyTerminals) {
        if (terminal->degree() >= 2) {
            const edge e = minCostIncidentEdge1[terminal];
            const node closestAdjacentNode = e->opposite(terminal);
            T distance {voronoiRegions.seed(closestAdjacentNode) == terminal
                            ? distanceToClosestTerminal[terminal]
                            : m_copyGraph.weight(e) + voronoiRegions.distance(closestAdjacentNode)};
 
            if (m_eps.geq(m_copyGraph.weight(minCostIncidentEdge2[terminal]), distance)
                    && !willBeAddedInSolution[e]) {
                edgesToBeAddedInSolution.pushBack(e);
                willBeAddedInSolution[e] = true;
            }
        }
    }
 
    return addEdgesToSolution(edgesToBeAddedInSolution);
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::shortLinksTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    OGDF_ASSERT(isConnected(m_copyGraph));
 
    Voronoi<T> voronoiRegions(m_copyGraph, m_copyGraph.edgeWeights(), m_copyTerminals);
 
    NodeArray<edge> minCostLeavingRegionEdge1(m_copyGraph, nullptr);
    NodeArray<edge> minCostLeavingRegionEdge2(m_copyGraph, nullptr);
 
    // populate minCostLeavingRegions{1,2}
    for (edge e : m_copyGraph.edges) {
        auto updateMinCostLeavingRegionsFor = [&](node seed) {
            if (minCostLeavingRegionEdge1[seed] == nullptr
                    || m_copyGraph.weight(minCostLeavingRegionEdge1[seed]) > m_copyGraph.weight(e)) {
                minCostLeavingRegionEdge2[seed] = minCostLeavingRegionEdge1[seed];
                minCostLeavingRegionEdge1[seed] = e;
            } else if (minCostLeavingRegionEdge2[seed] == nullptr
                    || m_copyGraph.weight(minCostLeavingRegionEdge2[seed]) > m_copyGraph.weight(e)) {
                minCostLeavingRegionEdge2[seed] = e;
            }
        };
        const node x = e->source(), y = e->target();
        const node seedX = voronoiRegions.seed(x), seedY = voronoiRegions.seed(y);
        if (seedX != seedY) { // e is a link between Voronoi regions
            // update minCostLeavingRegions for both x and y
            updateMinCostLeavingRegionsFor(seedX);
            updateMinCostLeavingRegionsFor(seedY);
        }
    }
 
    List<edge> edgesToBeAddedInSolution;
    EdgeArray<bool> willBeAddedInSolution(m_copyGraph, false);
    for (node terminal : m_copyTerminals) {
        if (minCostLeavingRegionEdge2[terminal] == nullptr) {
            continue;
        }
        // XXX: hm, is that smart? If there is no second shortest edge, then the first shortest edge belongs to the solution, doesn't it?
 
        const edge e1 = minCostLeavingRegionEdge1[terminal];
        const node x = e1->source(), y = e1->target();
        if (m_eps.geq(m_copyGraph.weight(minCostLeavingRegionEdge2[terminal]),
                    voronoiRegions.distance(x) + m_copyGraph.weight(e1) + voronoiRegions.distance(y))
                && !willBeAddedInSolution[e1]) {
            edgesToBeAddedInSolution.pushBack(e1);
            willBeAddedInSolution[e1] = true;
        }
    }
 
    return addEdgesToSolution(edgesToBeAddedInSolution);
}
 
template<typename T>
void SteinerTreePreprocessing<T>::computeRadiusOfTerminals(NodeArray<T>& terminalRadius) const {
    OGDF_ASSERT(m_copyTerminals.size() > 1);
 
    // compute the Voronoi regions
    Voronoi<T> voronoiRegions(m_copyGraph, m_copyGraph.edgeWeights(), m_copyTerminals);
 
    // compute the radius for each terminal
    terminalRadius.init(m_copyGraph, std::numeric_limits<T>::max());
    for (node v : m_copyGraph.nodes) {
        node seedV = voronoiRegions.seed(v);
        T distanceToSeedV = voronoiRegions.distance(v);
 
        for (adjEntry adj : v->adjEntries) {
            edge e = adj->theEdge();
            node adjacentNode = e->opposite(v);
 
            if (voronoiRegions.seed(adjacentNode) != seedV) {
                Math::updateMin(terminalRadius[seedV], distanceToSeedV + m_copyGraph.weight(e));
            }
        }
    }
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::deleteNodesAboveUpperBound(const NodeArray<T>& lowerBoundWithNode,
        const T upperBound) {
    bool changed = false;
    for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
        nextV = v->succ();
        if (m_eps.greater(lowerBoundWithNode[v], upperBound)) {
            OGDF_ASSERT(!m_copyIsTerminal[v]);
            m_copyGraph.delNode(v);
            changed = true;
        }
    }
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::lowerBoundBasedTest(T upperBound) {
    OGDF_ASSERT(!m_copyGraph.empty());
    if (m_copyTerminals.size() <= 1) {
        return false;
    }
 
    OGDF_ASSERT(isConnected(m_copyGraph));
 
    NodeArray<T> lowerBoundWithNode(m_copyGraph, std::numeric_limits<T>::lowest());
 
    NodeArray<List<std::pair<node, T>>> closestTerminals;
    computeClosestKTerminals(3, closestTerminals);
 
    // Update the lowerbound of the cost of a Steiner tree containing one particular node
    // as explained in [PV01, page 278, Observation 3.5]
    const T radiusSum = computeRadiusSum();
    for (node v : m_copyGraph.nodes) {
        if (m_copyIsTerminal[v]) {
            continue;
        }
 
        if (closestTerminals[v].size() < 2) {
            lowerBoundWithNode[v] = std::numeric_limits<T>::max();
            continue;
        }
 
        std::pair<node, T> closestTerminalPair1 = *(closestTerminals[v].get(0)),
                           closestTerminalPair2 = *(closestTerminals[v].get(1));
        T distanceToClosestTerminal1 = closestTerminalPair1.second,
          distanceToClosestTerminal2 = closestTerminalPair2.second;
 
        Math::updateMax(lowerBoundWithNode[v],
                distanceToClosestTerminal1 + distanceToClosestTerminal2 + radiusSum);
    }
 
    // Compute lower bound for edges, see [PV01, page 278, Observation 3.5]
    EdgeArray<T> lowerBoundWithEdge(m_copyGraph, 0);
    for (edge e : m_copyGraph.edges) {
        node x = e->source(), y = e->target();
 
        T distanceToClosestTerminalX = (*closestTerminals[x].begin()).second;
        T distanceToClosestTerminalY = (*closestTerminals[y].begin()).second;
 
        Math::updateMax(lowerBoundWithEdge[e],
                m_copyGraph.weight(e) + distanceToClosestTerminalX + distanceToClosestTerminalY
                        + radiusSum);
    }
 
    // Update the lowerbound of the cost of a Steiner tree containing one particular node
    // as explained in [PV01, pages 279-280, Observation 3.8]
    Graph auxiliaryGraph;
    NodeArray<node> terminalInAuxiliaryGraph(m_copyGraph, nullptr);
    for (node terminal : m_copyTerminals) {
        node newAuxiliaryNode = auxiliaryGraph.newNode();
        terminalInAuxiliaryGraph[terminal] = newAuxiliaryNode;
    }
 
    EdgeArray<T> initialEdgeWeight(m_copyGraph);
    for (edge e : m_copyGraph.edges) {
        initialEdgeWeight[e] = m_copyGraph.weight(e);
    }
    Voronoi<T> voronoiRegions(m_copyGraph, initialEdgeWeight, m_copyTerminals);
 
    std::unordered_map<NodePair, edge, steiner_tree::UnorderedNodePairHasher,
            steiner_tree::UnorderedNodePairEquality>
            edgeBetweenNodes;
    EdgeArray<T> edgeWeight(auxiliaryGraph, std::numeric_limits<T>::max());
    for (edge e : m_copyGraph.edges) {
        node x = e->source(), y = e->target();
        node seedX = voronoiRegions.seed(x), seedY = voronoiRegions.seed(y);
        if (seedX == seedY) {
            continue;
        }
 
        auto pair = NodePair(terminalInAuxiliaryGraph[seedX], terminalInAuxiliaryGraph[seedY]);
        if (edgeBetweenNodes.find(pair) == edgeBetweenNodes.end()) {
            edgeBetweenNodes[pair] = auxiliaryGraph.newEdge(terminalInAuxiliaryGraph[seedX],
                    terminalInAuxiliaryGraph[seedY]);
        }
        edge auxiliaryEdge = edgeBetweenNodes[pair];
        Math::updateMin(edgeWeight[auxiliaryEdge],
                min(voronoiRegions.distance(x), voronoiRegions.distance(y)) + m_copyGraph.weight(e));
    }
 
    EdgeArray<bool> isInTree(auxiliaryGraph, false);
    T minimumSpanningTreeCost = computeMinST(auxiliaryGraph, edgeWeight, isInTree);
    T longestEdgeCost = std::numeric_limits<T>::lowest();
    for (edge e : auxiliaryGraph.edges) {
        if (isInTree[e]) {
            Math::updateMax(longestEdgeCost, edgeWeight[e]);
        }
    }
 
    for (node v : m_copyGraph.nodes) {
        if (m_copyIsTerminal[v] || closestTerminals[v].size() < 2) {
            continue;
        }
 
        std::pair<node, T> closestTerminalPair1 = *(closestTerminals[v].get(0)),
                           closestTerminalPair2 = *(closestTerminals[v].get(1));
        T distanceToClosestTerminal1 = closestTerminalPair1.second,
          distanceToClosestTerminal2 = closestTerminalPair2.second;
 
        Math::updateMax(lowerBoundWithNode[v],
                minimumSpanningTreeCost - longestEdgeCost + distanceToClosestTerminal1
                        + distanceToClosestTerminal2);
    }
 
    return deleteNodesAboveUpperBound(lowerBoundWithNode, upperBound)
            || deleteEdgesAboveUpperBound(lowerBoundWithEdge, upperBound);
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::dualAscentBasedTest(int repetitions, T upperBound) {
    OGDF_ASSERT(!m_copyGraph.empty());
    bool changed = false;
    if (m_copyTerminals.size() > 1) {
        NodeArray<T> lowerBoundNodes;
        EdgeArray<T> lowerBoundEdges;
        SteinerTreeLowerBoundDualAscent<T> alg;
        alg.setRepetitions(repetitions);
        alg.call(m_copyGraph, m_copyTerminals, lowerBoundNodes, lowerBoundEdges);
 
        changed |= deleteNodesAboveUpperBound(lowerBoundNodes, upperBound);
        changed |= deleteEdgesAboveUpperBound(lowerBoundEdges, upperBound);
    }
    return changed;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::deleteEdgesAboveUpperBound(const EdgeArray<T>& lowerBoundWithEdge,
        const T upperBound) {
    bool changed = false;
    for (edge e = m_copyGraph.firstEdge(), nextE; e; e = nextE) {
        nextE = e->succ();
        if (m_eps.greater(lowerBoundWithEdge[e], upperBound)) {
            m_copyGraph.delEdge(e);
            changed = true;
        }
    }
    return changed;
}
 
template<typename T>
T SteinerTreePreprocessing<T>::computeRadiusSum() const {
    NodeArray<T> terminalRadius;
    computeRadiusOfTerminals(terminalRadius);
 
    // instead of sorting, we can simply ignore the two largest radii
    T radiusSum = T();
    T largestRadius1 = std::numeric_limits<T>::lowest(),
      largestRadius2 = std::numeric_limits<T>::lowest();
    for (node terminal : m_copyTerminals) {
        radiusSum += terminalRadius[terminal];
 
        if (terminalRadius[terminal] > largestRadius1) {
            largestRadius2 = largestRadius1;
            largestRadius1 = terminalRadius[terminal];
        } else {
            if (terminalRadius[terminal] > largestRadius2) {
                largestRadius2 = terminalRadius[terminal];
            }
        }
    }
    radiusSum -= largestRadius1 + largestRadius2;
    return radiusSum;
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::reachabilityTest(int maxDegreeTest, const int k) {
    OGDF_ASSERT(!m_copyGraph.empty());
    OGDF_ASSERT(isSimpleUndirected(m_copyGraph));
    OGDF_ASSERT(isConnected(m_copyGraph));
    bool changed = false;
    if (maxDegreeTest <= 0) {
        maxDegreeTest = m_copyGraph.numberOfNodes();
    }
 
    EdgeWeightedGraphCopy<T>* approximatedSteinerTree;
    T upperBoundCost = computeMinSteinerTreeUpperBound(approximatedSteinerTree);
 
    NodeArray<bool> isInUpperBoundTree(m_copyGraph, false);
    for (node v : approximatedSteinerTree->nodes) {
        isInUpperBoundTree[approximatedSteinerTree->original(v)] = true;
    }
    delete approximatedSteinerTree;
 
    // Initialize tprime and its hpd decomposition used for partially not adding useless edges during nodes' deletion
    EdgeWeightedGraphCopy<T> tprime;
    steiner_tree::constructTerminalSpanningTreeUsingVoronoiRegions(tprime, m_copyGraph,
            m_copyTerminals);
    OGDF_ASSERT(!tprime.empty());
 
    NodeArray<List<std::pair<node, T>>> closestTerminals;
    computeClosestKTerminals(k, closestTerminals);
 
    steiner_tree::HeavyPathDecomposition<T> tprimeHPD(tprime);
 
    // check which nodes can be deleted
    for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
        nextV = v->succ();
 
        if (isInUpperBoundTree[v] || v->degree() > maxDegreeTest) {
            continue;
        }
 
        // compute v's farthest and closest terminals
        Dijkstra<T> dijkstra;
 
        NodeArray<T> distance(m_copyGraph);
        NodeArray<edge> predecessor(m_copyGraph, nullptr);
        dijkstra.call(m_copyGraph, m_copyGraph.edgeWeights(), v, predecessor, distance);
 
        // compute first, second nearest terminals and farthest terminal
        node farthestTerminal = nullptr;
        T distanceToFarthestTerminal(0);
        T distanceToClosestTerminal1 = std::numeric_limits<T>::max(),
          distanceToClosestTerminal2 = std::numeric_limits<T>::max();
        for (node terminal : m_copyTerminals) {
            if (distanceToFarthestTerminal < distance[terminal]) {
                farthestTerminal = terminal;
                distanceToFarthestTerminal = distance[terminal];
            }
 
            if (distanceToClosestTerminal1 > distance[terminal]) {
                distanceToClosestTerminal2 = distanceToClosestTerminal1;
                distanceToClosestTerminal1 = distance[terminal];
            } else {
                if (distanceToClosestTerminal2 > distance[terminal]) {
                    distanceToClosestTerminal2 = distance[terminal];
                }
            }
        }
 
        if (predecessor[farthestTerminal] == nullptr // is not in the same component with the terminals
                || distanceToClosestTerminal2
                        == std::numeric_limits<T>::max() // cannot reach at least 2 terminals, must be deleted
                || m_eps.geq(distanceToFarthestTerminal + distanceToClosestTerminal1
                                + distanceToClosestTerminal2,
                        upperBoundCost)) {
            changed = true;
            // delete the node
            if (predecessor[farthestTerminal] != nullptr
                    && distanceToClosestTerminal2 != std::numeric_limits<T>::max()
                    && m_eps.less(distanceToFarthestTerminal + distanceToClosestTerminal1,
                            upperBoundCost)) {
                // the deleted node has degree 2 -> replace it with edges
                deleteSteinerDegreeTwoNode(v, tprime, tprimeHPD, closestTerminals);
            } else {
                // just delete the node
                m_copyGraph.delNode(v);
            }
        }
    }
 
    return changed;
}
 
template<typename T>
template<typename LAMBDA>
void SteinerTreePreprocessing<T>::computeOptimalTerminals(node v, LAMBDA dist,
        node& optimalTerminal1, node& optimalTerminal2, NodeArray<T>& distance) const {
    // run Dijkstra starting from v
    Dijkstra<T> dijkstra;
 
    distance.init(m_copyGraph);
    NodeArray<edge> predecessor(m_copyGraph, nullptr);
    dijkstra.call(m_copyGraph, m_copyGraph.edgeWeights(), v, predecessor, distance);
 
    for (node terminal : m_copyTerminals) {
        if (predecessor[terminal] == nullptr) {
            continue;
        }
 
        if (optimalTerminal1 == nullptr
                || dist(optimalTerminal1, distance) > dist(terminal, distance)) {
            optimalTerminal2 = optimalTerminal1;
            optimalTerminal1 = terminal;
        } else {
            if (optimalTerminal2 == nullptr
                    || dist(optimalTerminal2, distance) > dist(terminal, distance)) {
                optimalTerminal2 = terminal;
            }
        }
    }
    OGDF_ASSERT(optimalTerminal1 != nullptr);
    OGDF_ASSERT(optimalTerminal2 != nullptr);
    OGDF_ASSERT(optimalTerminal1 != optimalTerminal2);
}
 
template<typename T>
bool SteinerTreePreprocessing<T>::cutReachabilityTest() {
    OGDF_ASSERT(!m_copyGraph.empty());
    if (m_copyTerminals.size() <= 2) {
        return false;
    }
 
    // get the upper bound
    EdgeWeightedGraphCopy<T>* approximatedSteinerTree;
    const T upperBoundCost = computeMinSteinerTreeUpperBound(approximatedSteinerTree);
 
    NodeArray<bool> isInUpperBoundTree(m_copyGraph, false);
    for (node v : approximatedSteinerTree->nodes) {
        isInUpperBoundTree[approximatedSteinerTree->original(v)] = true;
    }
    delete approximatedSteinerTree;
 
    T cK = T();
    NodeArray<T> minCostOfAdjacentEdge(m_copyGraph, std::numeric_limits<T>::max());
    for (node terminal : m_copyTerminals) {
        for (adjEntry adj : terminal->adjEntries) {
            Math::updateMin(minCostOfAdjacentEdge[terminal], m_copyGraph.weight(adj->theEdge()));
        }
        cK += minCostOfAdjacentEdge[terminal];
    }
    auto dist = [&minCostOfAdjacentEdge](node terminal, const NodeArray<T>& distance) {
        return distance[terminal] - minCostOfAdjacentEdge[terminal];
    };
 
    List<node> delNodes;
    std::set<edge> delEdges;
    NodeArray<T> vDistance;
    NodeArray<T> wDistance;
    for (node v = m_copyGraph.firstNode(), nextV; v; v = nextV) {
        nextV = v->succ();
 
        if (isInUpperBoundTree[v]) {
            continue;
        }
 
        // compute its optimal terminals
        node vOptimalTerminal1 = nullptr, vOptimalTerminal2 = nullptr;
        computeOptimalTerminals(v, dist, vOptimalTerminal1, vOptimalTerminal2, vDistance);
 
        // check whether it can be deleted
        if (m_eps.geq(cK + dist(vOptimalTerminal1, vDistance) + dist(vOptimalTerminal2, vDistance),
                    upperBoundCost)) {
            delNodes.pushBack(v);
        } else { // it is not deleted, perform the edge test
            for (adjEntry adj = v->firstAdj(), adjNext; adj; adj = adjNext) {
                adjNext = adj->succ();
                node w = adj->twinNode();
                if (m_copyIsTerminal[w]) {
                    continue;
                }
                node wOptimalTerminal1 = nullptr, wOptimalTerminal2 = nullptr;
                computeOptimalTerminals(w, dist, wOptimalTerminal1, wOptimalTerminal2, wDistance);
 
                node vOptimalTerminal = vOptimalTerminal1;
                node wOptimalTerminal = wOptimalTerminal1;
                if (vOptimalTerminal == wOptimalTerminal) {
                    // the nearest terminals to v and w are the same, but they have to be
                    // different. Obtain the minimum choice such that they are different.
                    if (m_eps.leq(dist(vOptimalTerminal1, vDistance)
                                        + dist(wOptimalTerminal2, wDistance),
                                dist(vOptimalTerminal2, vDistance)
                                        + dist(wOptimalTerminal1, wDistance))) {
                        wOptimalTerminal = wOptimalTerminal2;
                    } else {
                        vOptimalTerminal = vOptimalTerminal2;
                    }
                }
                OGDF_ASSERT(vOptimalTerminal != wOptimalTerminal);
                if (m_eps.geq(cK + dist(vOptimalTerminal, vDistance) + dist(wOptimalTerminal, wDistance)
                                    + m_copyGraph.weight(adj->theEdge()),
                            upperBoundCost)) {
                    delEdges.insert(adj->theEdge());
                }
            }
        }
    }
 
    bool changed = false;
    for (edge e : delEdges) {
        m_copyGraph.delEdge(e);
        changed = true;
    }
    for (node v : delNodes) {
        m_copyGraph.delNode(v);
        changed = true;
    }
    return changed;
}
 
}