/* -*- mode: C++; indent-tabs-mode: nil; -*-

  *

  * This file is a part of LEMON, a generic C++ optimization library.

  *

  * Copyright (C) 2003-2010

  * Egervary Jeno Kombinatorikus Optimalizalasi Kutatocsoport

  * (Egervary Research Group on Combinatorial Optimization, EGRES).

  *

  * Permission to use, modify and distribute this software is granted

  * provided that this copyright notice appears in all copies. For

  * precise terms see the accompanying LICENSE file.

  *

  * This software is provided "AS IS" with no warranty of any kind,

  * express or implied, and with no claim as to its suitability for any

  * purpose.

  *

  */

 #ifndef LEMON_GROSSO_LOCATELLI_PULLAN_MC_H

 #define LEMON_GROSSO_LOCATELLI_PULLAN_MC_H

 /// \ingroup approx_algs

 ///

 /// \file

 /// \brief The iterated local search algorithm of Grosso, Locatelli, and Pullan

 /// for the maximum clique problem

 #include <vector>

 #include <limits>

 #include <lemon/core.h>

 #include <lemon/random.h>

 namespace lemon {

   /// \addtogroup approx_algs

   /// @{

   /// \brief Implementation of the iterated local search algorithm of Grosso,

   /// Locatelli, and Pullan for the maximum clique problem

   ///

   /// \ref GrossoLocatelliPullanMc implements the iterated local search

   /// algorithm of Grosso, Locatelli, and Pullan for solving the \e maximum

   /// \e clique \e problem \cite grosso08maxclique.

   /// It is to find the largest complete subgraph (\e clique) in an

   /// undirected graph, i.e., the largest set of nodes where each

   /// pair of nodes is connected.

   ///

   /// This class provides a simple but highly efficient and robust heuristic

   /// method that quickly finds a quite large clique, but not necessarily the

   /// largest one.

   /// The algorithm performs a certain number of iterations to find several

   /// cliques and selects the largest one among them. Various limits can be

   /// specified to control the running time and the effectiveness of the

   /// search process.

   ///

   /// \tparam GR The undirected graph type the algorithm runs on.

   ///

   /// \note %GrossoLocatelliPullanMc provides three different node selection

   /// rules, from which the most powerful one is used by default.

   /// For more information, see \ref SelectionRule.

   template <typename GR>

   class GrossoLocatelliPullanMc

   {

   public:

     /// \brief Constants for specifying the node selection rule.

     ///

     /// Enum type containing constants for specifying the node selection rule

     /// for the \ref run() function.

     ///

     /// During the algorithm, nodes are selected for addition to the current

     /// clique according to the applied rule.

     /// In general, the PENALTY_BASED rule turned out to be the most powerful

     /// and the most robust, thus it is the default option.

     /// However, another selection rule can be specified using the \ref run()

     /// function with the proper parameter.

     enum SelectionRule {

       /// A node is selected randomly without any evaluation at each step.

       RANDOM,

       /// A node of maximum degree is selected randomly at each step.

       DEGREE_BASED,

       /// A node of minimum penalty is selected randomly at each step.

       /// The node penalties are updated adaptively after each stage of the

       /// search process.

       PENALTY_BASED

     };

     /// \brief Constants for the causes of search termination.

     ///

     /// Enum type containing constants for the different causes of search

     /// termination. The \ref run() function returns one of these values.

     enum TerminationCause {

       /// The iteration count limit is reached.

       ITERATION_LIMIT,

       /// The step count limit is reached.

       STEP_LIMIT,

       /// The clique size limit is reached.

       SIZE_LIMIT

     };

   private:

     TEMPLATE_GRAPH_TYPEDEFS(GR);

     typedef std::vector<int> IntVector;

     typedef std::vector<char> BoolVector;

     typedef std::vector<BoolVector> BoolMatrix;

     // Note: vector<char> is used instead of vector<bool> for efficiency reasons

     // The underlying graph

     const GR &_graph;

     IntNodeMap _id;

     // Internal matrix representation of the graph

     BoolMatrix _gr;

     int _n;

     // Search options

     bool _delta_based_restart;

     int _restart_delta_limit;

     // Search limits

     int _iteration_limit;

     int _step_limit;

     int _size_limit;

     // The current clique

     BoolVector _clique;

     int _size;

     // The best clique found so far

     BoolVector _best_clique;

     int _best_size;

     // The "distances" of the nodes from the current clique.

     // _delta[u] is the number of nodes in the clique that are

     // not connected with u.

     IntVector _delta;

     // The current tabu set

     BoolVector _tabu;

     // Random number generator

     Random _rnd;

   private:

     // Implementation of the RANDOM node selection rule.

     class RandomSelectionRule

     {

     private:

       // References to the algorithm instance

       const BoolVector &_clique;

       const IntVector  &_delta;

       const BoolVector &_tabu;

       Random &_rnd;

       // Pivot rule data

       int _n;

     public:

       // Constructor

       RandomSelectionRule(GrossoLocatelliPullanMc &mc) :

         _clique(mc._clique), _delta(mc._delta), _tabu(mc._tabu),

         _rnd(mc._rnd), _n(mc._n)

       {}

       // Return a node index for a feasible add move or -1 if no one exists

       int nextFeasibleAddNode() const {

         int start_node = _rnd[_n];

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0 && !_tabu[i]) return i;

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0 && !_tabu[i]) return i;

         }

         return -1;

       }

       // Return a node index for a feasible swap move or -1 if no one exists

       int nextFeasibleSwapNode() const {

         int start_node = _rnd[_n];

         for (int i = start_node; i != _n; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i]) return i;

         }

         for (int i = 0; i != start_node; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i]) return i;

         }

         return -1;

       }

       // Return a node index for an add move or -1 if no one exists

       int nextAddNode() const {

         int start_node = _rnd[_n];

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0) return i;

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0) return i;

         }

         return -1;

       }

       // Update internal data structures between stages (if necessary)

       void update() {}

     }; //class RandomSelectionRule

     // Implementation of the DEGREE_BASED node selection rule.

     class DegreeBasedSelectionRule

     {

     private:

       // References to the algorithm instance

       const BoolVector &_clique;

       const IntVector  &_delta;

       const BoolVector &_tabu;

       Random &_rnd;

       // Pivot rule data

       int _n;

       IntVector _deg;

     public:

       // Constructor

       DegreeBasedSelectionRule(GrossoLocatelliPullanMc &mc) :

         _clique(mc._clique), _delta(mc._delta), _tabu(mc._tabu),

         _rnd(mc._rnd), _n(mc._n), _deg(_n)

       {

         for (int i = 0; i != _n; i++) {

           int d = 0;

           BoolVector &row = mc._gr[i];

           for (int j = 0; j != _n; j++) {

             if (row[j]) d++;

           }

           _deg[i] = d;

         }

       }

       // Return a node index for a feasible add move or -1 if no one exists

       int nextFeasibleAddNode() const {

         int start_node = _rnd[_n];

         int node = -1, max_deg = -1;

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0 && !_tabu[i] && _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0 && !_tabu[i] && _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         return node;

       }

       // Return a node index for a feasible swap move or -1 if no one exists

       int nextFeasibleSwapNode() const {

         int start_node = _rnd[_n];

         int node = -1, max_deg = -1;

         for (int i = start_node; i != _n; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i] &&

               _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i] &&

               _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         return node;

       }

       // Return a node index for an add move or -1 if no one exists

       int nextAddNode() const {

         int start_node = _rnd[_n];

         int node = -1, max_deg = -1;

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0 && _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0 && _deg[i] > max_deg) {

             node = i;

             max_deg = _deg[i];

           }

         }

         return node;

       }

       // Update internal data structures between stages (if necessary)

       void update() {}

     }; //class DegreeBasedSelectionRule

     // Implementation of the PENALTY_BASED node selection rule.

     class PenaltyBasedSelectionRule

     {

     private:

       // References to the algorithm instance

       const BoolVector &_clique;

       const IntVector  &_delta;

       const BoolVector &_tabu;

       Random &_rnd;

       // Pivot rule data

       int _n;

       IntVector _penalty;

     public:

       // Constructor

       PenaltyBasedSelectionRule(GrossoLocatelliPullanMc &mc) :

         _clique(mc._clique), _delta(mc._delta), _tabu(mc._tabu),

         _rnd(mc._rnd), _n(mc._n), _penalty(_n, 0)

       {}

       // Return a node index for a feasible add move or -1 if no one exists

       int nextFeasibleAddNode() const {

         int start_node = _rnd[_n];

         int node = -1, min_p = std::numeric_limits<int>::max();

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0 && !_tabu[i] && _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0 && !_tabu[i] && _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         return node;

       }

       // Return a node index for a feasible swap move or -1 if no one exists

       int nextFeasibleSwapNode() const {

         int start_node = _rnd[_n];

         int node = -1, min_p = std::numeric_limits<int>::max();

         for (int i = start_node; i != _n; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i] &&

               _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (!_clique[i] && _delta[i] == 1 && !_tabu[i] &&

               _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         return node;

       }

       // Return a node index for an add move or -1 if no one exists

       int nextAddNode() const {

         int start_node = _rnd[_n];

         int node = -1, min_p = std::numeric_limits<int>::max();

         for (int i = start_node; i != _n; i++) {

           if (_delta[i] == 0 && _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         for (int i = 0; i != start_node; i++) {

           if (_delta[i] == 0 && _penalty[i] < min_p) {

             node = i;

             min_p = _penalty[i];

           }

         }

         return node;

       }

       // Update internal data structures between stages (if necessary)

       void update() {}

     }; //class PenaltyBasedSelectionRule

   public:

     /// \brief Constructor.

     ///

     /// Constructor.

     /// The global \ref rnd "random number generator instance" is used

     /// during the algorithm.

     ///

     /// \param graph The undirected graph the algorithm runs on.

     GrossoLocatelliPullanMc(const GR& graph) :

       _graph(graph), _id(_graph), _rnd(rnd)

     {

       initOptions();

     }

     /// \brief Constructor with random seed.

     ///

     /// Constructor with random seed.

     ///

     /// \param graph The undirected graph the algorithm runs on.

     /// \param seed Seed value for the internal random number generator

     /// that is used during the algorithm.

     GrossoLocatelliPullanMc(const GR& graph, int seed) :

       _graph(graph), _id(_graph), _rnd(seed)

     {

       initOptions();

     }

     /// \brief Constructor with random number generator.

     ///

     /// Constructor with random number generator.

     ///

     /// \param graph The undirected graph the algorithm runs on.

     /// \param random A random number generator that is used during the

     /// algorithm.

     GrossoLocatelliPullanMc(const GR& graph, const Random& random) :

       _graph(graph), _id(_graph), _rnd(random)

     {

       initOptions();

     }

     /// \name Execution Control

     /// The \ref run() function can be used to execute the algorithm.\n

     /// The functions \ref iterationLimit(int), \ref stepLimit(int), and 

     /// \ref sizeLimit(int) can be used to specify various limits for the

     /// search process.

     /// @{

     /// \brief Sets the maximum number of iterations.

     ///

     /// This function sets the maximum number of iterations.

     /// Each iteration of the algorithm finds a maximal clique (but not

     /// necessarily the largest one) by performing several search steps

     /// (node selections).

     ///

     /// This limit controls the running time and the success of the

     /// algorithm. For larger values, the algorithm runs slower, but it more

     /// likely finds larger cliques. For smaller values, the algorithm is

     /// faster but probably gives worse results.

     /// 

     /// The default value is \c 1000.

     /// \c -1 means that number of iterations is not limited.

     ///

     /// \warning You should specify a reasonable limit for the number of

     /// iterations and/or the number of search steps.

     ///

     /// \return <tt>(*this)</tt>

     ///

     /// \sa stepLimit(int)

     /// \sa sizeLimit(int)

     GrossoLocatelliPullanMc& iterationLimit(int limit) {

       _iteration_limit = limit;

       return *this;

     }

     /// \brief Sets the maximum number of search steps.

     ///

     /// This function sets the maximum number of elementary search steps.

     /// Each iteration of the algorithm finds a maximal clique (but not

     /// necessarily the largest one) by performing several search steps

     /// (node selections).

     ///

     /// This limit controls the running time and the success of the

     /// algorithm. For larger values, the algorithm runs slower, but it more

     /// likely finds larger cliques. For smaller values, the algorithm is

     /// faster but probably gives worse results.

     /// 

     /// The default value is \c -1, which means that number of steps

     /// is not limited explicitly. However, the number of iterations is

     /// limited and each iteration performs a finite number of search steps.

     ///

     /// \warning You should specify a reasonable limit for the number of

     /// iterations and/or the number of search steps.

     ///

     /// \return <tt>(*this)</tt>

     ///

     /// \sa iterationLimit(int)

     /// \sa sizeLimit(int)

     GrossoLocatelliPullanMc& stepLimit(int limit) {

       _step_limit = limit;

       return *this;

     }

     /// \brief Sets the desired clique size.

     ///

     /// This function sets the desired clique size that serves as a search

     /// limit. If a clique of this size (or a larger one) is found, then the

     /// algorithm terminates.

     /// 

     /// This function is especially useful if you know an exact upper bound

     /// for the size of the cliques in the graph or if any clique above 

     /// a certain size limit is sufficient for your application.

     /// 

     /// The default value is \c -1, which means that the size limit is set to

     /// the number of nodes in the graph.

     ///

     /// \return <tt>(*this)</tt>

     ///

     /// \sa iterationLimit(int)

     /// \sa stepLimit(int)

     GrossoLocatelliPullanMc& sizeLimit(int limit) {

       _size_limit = limit;

       return *this;

     }

     /// \brief The maximum number of iterations.

     ///

     /// This function gives back the maximum number of iterations.

     /// \c -1 means that no limit is specified.

     ///

     /// \sa iterationLimit(int)

     int iterationLimit() const {

       return _iteration_limit;

     }

     /// \brief The maximum number of search steps.

     ///

     /// This function gives back the maximum number of search steps.

     /// \c -1 means that no limit is specified.

     ///

     /// \sa stepLimit(int)

     int stepLimit() const {

       return _step_limit;

     }

     /// \brief The desired clique size.

     ///

     /// This function gives back the desired clique size that serves as a

     /// search limit. \c -1 means that this limit is set to the number of

     /// nodes in the graph.

     ///

     /// \sa sizeLimit(int)

     int sizeLimit() const {

       return _size_limit;

     }

     /// \brief Runs the algorithm.

     ///

     /// This function runs the algorithm. If one of the specified limits

     /// is reached, the search process terminates.

     ///

     /// \param rule The node selection rule. For more information, see

     /// \ref SelectionRule.

     ///

     /// \return The termination cause of the search. For more information,

     /// see \ref TerminationCause.

     TerminationCause run(SelectionRule rule = PENALTY_BASED)

     {

       init();

       switch (rule) {

         case RANDOM:

           return start<RandomSelectionRule>();

         case DEGREE_BASED:

           return start<DegreeBasedSelectionRule>();

         default:

           return start<PenaltyBasedSelectionRule>();

       }

     }

     /// @}

     /// \name Query Functions

     /// The results of the algorithm can be obtained using these functions.\n

     /// The run() function must be called before using them. 

     /// @{

     /// \brief The size of the found clique

     ///

     /// This function returns the size of the found clique.

     ///

     /// \pre run() must be called before using this function.

     int cliqueSize() const {

       return _best_size;

     }

     /// \brief Gives back the found clique in a \c bool node map

     ///

     /// This function gives back the characteristic vector of the found

     /// clique in the given node map.

     /// It must be a \ref concepts::WriteMap "writable" node map with

     /// \c bool (or convertible) value type.

     ///

     /// \pre run() must be called before using this function.

     template <typename CliqueMap>

     void cliqueMap(CliqueMap &map) const {

       for (NodeIt n(_graph); n != INVALID; ++n) {

         map[n] = static_cast<bool>(_best_clique[_id[n]]);

       }

     }

     /// \brief Iterator to list the nodes of the found clique

     ///

     /// This iterator class lists the nodes of the found clique.

     /// Before using it, you must allocate a GrossoLocatelliPullanMc instance

     /// and call its \ref GrossoLocatelliPullanMc::run() "run()" method.

     ///

     /// The following example prints out the IDs of the nodes in the found

     /// clique.

     /// \code

     ///   GrossoLocatelliPullanMc<Graph> mc(g);

     ///   mc.run();

     ///   for (GrossoLocatelliPullanMc<Graph>::CliqueNodeIt n(mc);

     ///        n != INVALID; ++n)

     ///   {

     ///     std::cout << g.id(n) << std::endl;

     ///   }

     /// \endcode

     class CliqueNodeIt

     {

     private:

       NodeIt _it;

       BoolNodeMap _map;

     public:

       /// Constructor

       /// Constructor.

       /// \param mc The algorithm instance.

       CliqueNodeIt(const GrossoLocatelliPullanMc &mc)

        : _map(mc._graph)

       {

         mc.cliqueMap(_map);

         for (_it = NodeIt(mc._graph); _it != INVALID && !_map[_it]; ++_it) ;

       }

       /// Conversion to \c Node

       operator Node() const { return _it; }

       bool operator==(Invalid) const { return _it == INVALID; }

       bool operator!=(Invalid) const { return _it != INVALID; }

       /// Next node

       CliqueNodeIt &operator++() {

         for (++_it; _it != INVALID && !_map[_it]; ++_it) ;

         return *this;

       }

       /// Postfix incrementation

       /// Postfix incrementation.

       ///

       /// \warning This incrementation returns a \c Node, not a

       /// \c CliqueNodeIt as one may expect.

       typename GR::Node operator++(int) {

         Node n=*this;

         ++(*this);

         return n;

       }

     };

     /// @}

   private:

     // Initialize search options and limits

     void initOptions() {

       // Search options

       _delta_based_restart = true;

       _restart_delta_limit = 4;

       // Search limits

       _iteration_limit = 1000;

       _step_limit = -1;             // this is disabled by default

       _size_limit = -1;             // this is disabled by default

     }

     // Adds a node to the current clique

     void addCliqueNode(int u) {

       if (_clique[u]) return;

       _clique[u] = true;

       _size++;

       BoolVector &row = _gr[u];

       for (int i = 0; i != _n; i++) {

         if (!row[i]) _delta[i]++;

       }

     }

     // Removes a node from the current clique

     void delCliqueNode(int u) {

       if (!_clique[u]) return;

       _clique[u] = false;

       _size--;

       BoolVector &row = _gr[u];

       for (int i = 0; i != _n; i++) {

         if (!row[i]) _delta[i]--;

       }

     }

     // Initialize data structures

     void init() {

       _n = countNodes(_graph);

       int ui = 0;

       for (NodeIt u(_graph); u != INVALID; ++u) {

         _id[u] = ui++;

       }

       _gr.clear();

       _gr.resize(_n, BoolVector(_n, false));

       ui = 0;

       for (NodeIt u(_graph); u != INVALID; ++u) {

         for (IncEdgeIt e(_graph, u); e != INVALID; ++e) {

           int vi = _id[_graph.runningNode(e)];

           _gr[ui][vi] = true;

           _gr[vi][ui] = true;

         }

         ++ui;

       }

       _clique.clear();

       _clique.resize(_n, false);

       _size = 0;

       _best_clique.clear();

       _best_clique.resize(_n, false);

       _best_size = 0;

       _delta.clear();

       _delta.resize(_n, 0);

       _tabu.clear();

       _tabu.resize(_n, false);

     }

     // Executes the algorithm

     template <typename SelectionRuleImpl>

     TerminationCause start() {

       if (_n == 0) return SIZE_LIMIT;

       if (_n == 1) {

         _best_clique[0] = true;

         _best_size = 1;

         return SIZE_LIMIT;

       }

       // Iterated local search algorithm

       const int max_size = _size_limit >= 0 ? _size_limit : _n;

       const int max_restart = _iteration_limit >= 0 ?

         _iteration_limit : std::numeric_limits<int>::max();

       const int max_select = _step_limit >= 0 ?

         _step_limit : std::numeric_limits<int>::max();

       SelectionRuleImpl sel_method(*this);

       int select = 0, restart = 0;

       IntVector restart_nodes;

       while (select < max_select && restart < max_restart) {

         // Perturbation/restart

         restart++;

         if (_delta_based_restart) {

           restart_nodes.clear();

           for (int i = 0; i != _n; i++) {

             if (_delta[i] >= _restart_delta_limit)

               restart_nodes.push_back(i);

           }

         }

         int rs_node = -1;

         if (restart_nodes.size() > 0) {

           rs_node = restart_nodes[_rnd[restart_nodes.size()]];

         } else {

           rs_node = _rnd[_n];

         }

         BoolVector &row = _gr[rs_node];

         for (int i = 0; i != _n; i++) {

           if (_clique[i] && !row[i]) delCliqueNode(i);

         }

         addCliqueNode(rs_node);

         // Local search

         _tabu.clear();

         _tabu.resize(_n, false);

         bool tabu_empty = true;

         int max_swap = _size;

         while (select < max_select) {

           select++;

           int u;

           if ((u = sel_method.nextFeasibleAddNode()) != -1) {

             // Feasible add move

             addCliqueNode(u);

             if (tabu_empty) max_swap = _size;

           }

           else if ((u = sel_method.nextFeasibleSwapNode()) != -1) {

             // Feasible swap move

             int v = -1;

             BoolVector &row = _gr[u];

             for (int i = 0; i != _n; i++) {

               if (_clique[i] && !row[i]) {

                 v = i;

                 break;

               }

             }

             addCliqueNode(u);

             delCliqueNode(v);

             _tabu[v] = true;

             tabu_empty = false;

             if (--max_swap <= 0) break;

           }

           else if ((u = sel_method.nextAddNode()) != -1) {

             // Non-feasible add move

             addCliqueNode(u);

           }

           else break;

         }

         if (_size > _best_size) {

           _best_clique = _clique;

           _best_size = _size;

           if (_best_size >= max_size) return SIZE_LIMIT;

         }

         sel_method.update();

       }

       return (restart >= max_restart ? ITERATION_LIMIT : STEP_LIMIT);

     }

   }; //class GrossoLocatelliPullanMc

   ///@}

 } //namespace lemon

 #endif //LEMON_GROSSO_LOCATELLI_PULLAN_MC_H