/* -*- C++ -*-

 *

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

 *

 * Copyright (C) 2003-2007

 * 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_MIN_MEAN_CYCLE_H

#define LEMON_MIN_MEAN_CYCLE_H

/// \ingroup min_cost_flow

///

/// \file

/// \brief Karp's algorithm for finding a minimum mean (directed) cycle.

#include <vector>

#include <lemon/graph_utils.h>

#include <lemon/topology.h>

#include <lemon/path.h>

namespace lemon {

  /// \addtogroup min_cost_flow

  /// @{

  /// \brief Implementation of Karp's algorithm for finding a

  /// minimum mean (directed) cycle.

  ///

  /// The \ref lemon::MinMeanCycle "MinMeanCycle" implements Karp's

  /// algorithm for finding a minimum mean (directed) cycle.

  ///

  /// \param Graph The directed graph type the algorithm runs on.

  /// \param LengthMap The type of the length (cost) map.

  ///

  /// \author Peter Kovacs

  template <typename Graph,

    typename LengthMap = typename Graph::template EdgeMap<int> >

  class MinMeanCycle

  {

    typedef typename Graph::Node Node;

    typedef typename Graph::NodeIt NodeIt;

    typedef typename Graph::Edge Edge;

    typedef typename Graph::EdgeIt EdgeIt;

    typedef typename Graph::OutEdgeIt OutEdgeIt;

    typedef typename LengthMap::Value Length;

    typedef typename Graph::template NodeMap<int> IntNodeMap;

    typedef typename Graph::template NodeMap<Edge> PredNodeMap;

    typedef Path<Graph> Path;

    typedef std::vector<Node> NodeVector;

  protected:

    /// \brief Data structure for path data.

    struct PathData

    {

      bool found;

      Length dist;

      Edge pred;

      PathData(bool _found = false, Length _dist = 0) :

	found(_found), dist(_dist), pred(INVALID) {}

      PathData(bool _found, Length _dist, Edge _pred) :

	found(_found), dist(_dist), pred(_pred) {}

    };

  private:

    typedef typename Graph::template NodeMap<std::vector<PathData> >

      PathDataNodeMap;

  protected:

    /// \brief Node map for storing path data.

    ///

    /// Node map for storing path data of all nodes in the current

    /// component. dmap[v][k] is the length of a shortest directed walk

    /// to node v from the starting node containing exactly k edges.

    PathDataNodeMap dmap;

    /// \brief The directed graph the algorithm runs on.

    const Graph &graph;

    /// \brief The length of the edges.

    const LengthMap &length;

    /// \brief The total length of the found cycle.

    Length cycle_length;

    /// \brief The number of edges in the found cycle.

    int cycle_size;

    /// \brief A node for obtaining a minimum mean cycle.

    Node cycle_node;

    /// \brief The found cycle.

    Path *cycle_path;

    /// \brief The algorithm uses local \ref lemon::Path "Path"

    /// structure to store the found cycle.

    bool local_path;

    /// \brief Node map for identifying strongly connected components.

    IntNodeMap comp;

    /// \brief The number of strongly connected components.

    int comp_num;

    /// \brief Counter for identifying the current component.

    int comp_cnt;

    /// \brief Nodes of the current component.

    NodeVector nodes;

    /// \brief The processed nodes in the last round.

    NodeVector process;

  public :

    /// \brief The constructor of the class.

    ///

    /// The constructor of the class.

    ///

    /// \param _graph The directed graph the algorithm runs on.

    /// \param _length The length (cost) of the edges.

    MinMeanCycle( const Graph &_graph,

		  const LengthMap &_length ) :

      graph(_graph), length(_length), dmap(_graph), comp(_graph),

      cycle_length(0), cycle_size(-1), cycle_node(INVALID),

      cycle_path(NULL), local_path(false)

    { }

    /// \brief The destructor of the class.

    ~MinMeanCycle() {

      if (local_path) delete cycle_path;

    }

  protected:

    /// \brief Initializes the internal data structures for the current

    /// component.

    void initCurrent() {

      nodes.clear();

      // Finding the nodes of the current component

      for (NodeIt v(graph); v != INVALID; ++v) {

	if (comp[v] == comp_cnt) nodes.push_back(v);

      }

      // Creating vectors for all nodes

      int n = nodes.size();

      for (int i = 0; i < n; ++i) {

	dmap[nodes[i]].resize(n + 1);

      }

    }

    /// \brief Processes all rounds of computing required path data for

    /// the current component.

    void processRounds() {

      dmap[nodes[0]][0] = PathData(true, 0);

      process.clear();

      // Processing the first round

      for (OutEdgeIt e(graph, nodes[0]); e != INVALID; ++e) {

	Node v = graph.target(e);

	if (comp[v] != comp_cnt || v == nodes[0]) continue;

	dmap[v][1] = PathData(true, length[e], e);

	process.push_back(v);

      }

      // Processing other rounds

      int n = nodes.size(), k;

      for (k = 2; k <= n && process.size() < n; ++k)

	processNextBuildRound(k);

      for ( ; k <= n; ++k)

	processNextFullRound(k);

    }

    /// \brief Processes one round of computing required path data and

    /// rebuilds \ref process vector.

    void processNextBuildRound(int k) {

      NodeVector next;

      for (int i = 0; i < process.size(); ++i) {

	for (OutEdgeIt e(graph, process[i]); e != INVALID; ++e) {

	  Node v = graph.target(e);

	  if (comp[v] != comp_cnt) continue;

	  if (!dmap[v][k].found) {

	    next.push_back(v);

	    dmap[v][k] = PathData(true, dmap[process[i]][k-1].dist + length[e], e);

	  }

	  else if (dmap[process[i]][k-1].dist + length[e] < dmap[v][k].dist) {

	    dmap[v][k] = PathData(true, dmap[process[i]][k-1].dist + length[e], e);

	  }

	}

      }

      process.swap(next);

    }

    /// \brief Processes one round of computing required path data

    /// using \ref nodes vector instead of \ref process vector.

    void processNextFullRound(int k) {

      for (int i = 0; i < nodes.size(); ++i) {

	for (OutEdgeIt e(graph, nodes[i]); e != INVALID; ++e) {

	  Node v = graph.target(e);

	  if (comp[v] != comp_cnt) continue;

	  if ( !dmap[v][k].found ||

	       dmap[nodes[i]][k-1].dist + length[e] < dmap[v][k].dist ) {

	    dmap[v][k] = PathData(true, dmap[nodes[i]][k-1].dist + length[e], e);

	  }

	}

      }

    }

    /// \brief Finds the minimum cycle mean value in the current

    /// component.

    bool findCurrentMin(Length &min_length, int &min_size, Node &min_node) {

      bool found_min = false;

      for (int i = 0; i < nodes.size(); ++i) {

	int n = nodes.size();

	if (!dmap[nodes[i]][n].found) continue;

	Length len;

	int size;

	bool found_one = false;

	for (int k = 0; k < n; ++k) {

	  if (!dmap[nodes[i]][k].found) continue;

	  Length _len = dmap[nodes[i]][n].dist - dmap[nodes[i]][k].dist;

	  int _size = n - k;

	  if (!found_one || len * _size < _len * size) {

	    found_one = true;

	    len = _len;

	    size = _size;

	  }

	}

	if ( found_one &&

	     (!found_min || len * min_size < min_length * size) ) {

	  found_min = true;

	  min_length = len;

	  min_size = size;

	  min_node = nodes[i];

	}

      }

      return found_min;

    }

  public:

    /// \brief Runs the algorithm.

    ///

    /// Runs the algorithm.

    ///

    /// \return \c true if a cycle exists in the graph.

    ///

    /// \note Apart from the return value, <tt>m.run()</tt> is just a

    /// shortcut of the following code.

    /// \code

    ///   m.init();

    ///   m.findMinMean();

    ///   m.findCycle();

    /// \endcode

    bool run() {

      init();

      findMinMean();

      return findCycle();

    }

    /// \brief Initializes the internal data structures.

    ///

    /// Initializes the internal data structures.

    ///

    /// \sa reset()

    void init() {

      comp_num = stronglyConnectedComponents(graph, comp);

      if (!cycle_path) {

	local_path = true;

	cycle_path = new Path;

      }

    }

    /// \brief Finds the minimum cycle mean value in the graph.

    ///

    /// Computes all the required path data and finds the minimum cycle

    /// mean value in the graph.

    ///

    /// \return \c true if a cycle exists in the graph.

    ///

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

    bool findMinMean() {

      cycle_node = INVALID;

      for (comp_cnt = 0; comp_cnt < comp_num; ++comp_cnt) {

	initCurrent();

	processRounds();

	Length min_length;

	int min_size;

	Node min_node;

	bool found_min = findCurrentMin(min_length, min_size, min_node);

	if ( found_min && (cycle_node == INVALID ||

	     min_length * cycle_size < cycle_length * min_size) ) {

	  cycle_length = min_length;

	  cycle_size = min_size;

	  cycle_node = min_node;

	}

      }

      return (cycle_node != INVALID);

    }

    /// \brief Finds a critical (minimum mean) cycle.

    ///

    /// Finds a critical (minimum mean) cycle using the path data

    /// stored in \ref dmap.

    ///

    /// \return \c true if a cycle exists in the graph.

    ///

    /// \pre \ref init() and \ref findMinMean() must be called before

    /// using this function.

    bool findCycle() {

      if (cycle_node == INVALID) return false;

      cycle_length = 0;

      cycle_size = 0;

      IntNodeMap reached(graph, -1);

      int r = reached[cycle_node] = dmap[cycle_node].size() - 1;

      Node u = graph.source(dmap[cycle_node][r].pred);

      while (reached[u] < 0) {

	reached[u] = --r;

	u = graph.source(dmap[u][r].pred);

      }

      r = reached[u];

      Edge e = dmap[u][r].pred;

      cycle_path->addFront(e);

      cycle_length = cycle_length + length[e];

      ++cycle_size;

      Node v;

      while ((v = graph.source(e)) != u) {

	e = dmap[v][--r].pred;

	cycle_path->addFront(e);

	cycle_length = cycle_length + length[e];

	++cycle_size;

      }

      return true;

    }

    /// \brief Resets the internal data structures.

    ///

    /// Resets the internal data structures so that \ref findMinMean()

    /// and \ref findCycle() can be called again (e.g. when the

    /// underlaying graph has been modified).

    ///

    /// \sa init()

    void reset() {

      for (NodeIt u(graph); u != INVALID; ++u)

	dmap[u].clear();

      cycle_node = INVALID;

      if (cycle_path) cycle_path->clear();

      comp_num = stronglyConnectedComponents(graph, comp);

    }

    /// \brief Returns the total length of the found cycle.

    ///

    /// Returns the total length of the found cycle.

    ///

    /// \pre \ref run() or \ref findCycle() must be called before

    /// using this function. If only \ref findMinMean() is called,

    /// the return value is not valid.

    Length cycleLength() const {

      return cycle_length;

    }

    /// \brief Returns the number of edges in the found cycle.

    ///

    /// Returns the number of edges in the found cycle.

    ///

    /// \pre \ref run() or \ref findCycle() must be called before

    /// using this function. If only \ref findMinMean() is called,

    /// the return value is not valid.

    int cycleEdgeNum() const {

      return cycle_size;

    }

    /// \brief Returns the mean length of the found cycle.

    ///

    /// Returns the mean length of the found cycle.

    ///

    /// \pre \ref run() or \ref findMinMean() must be called before

    /// using this function.

    ///

    /// \warning LengthMap::Value must be convertible to double.

    ///

    /// \note <tt>m.minMean()</tt> is just a shortcut of the following

    /// code.

    /// \code

    ///   return m.cycleLength() / double(m.cycleEdgeNum());

    /// \endcode

    /// However if only \ref findMinMean() is called before using this

    /// function, <tt>m.cycleLength()</tt> and <tt>m.cycleEdgeNum()</tt>

    /// are not valid alone, only their ratio is valid.

    double minMean() const {

      return cycle_length / (double)cycle_size;

    }

    /// \brief Returns a const reference to the \ref lemon::Path "Path"

    /// structure of the found cycle.

    ///

    /// Returns a const reference to the \ref lemon::Path "Path"

    /// structure of the found cycle.

    ///

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

    ///

    /// \sa \ref cyclePath()

    const Path& cycle() const {

      return *cycle_path;

    }

    /// \brief Sets the \ref lemon::Path "Path" structure storing the

    /// found cycle.

    ///

    /// Sets the \ref lemon::Path "Path" structure storing the found

    /// cycle. If you don't use this function before calling

    /// \ref run(), it will allocate one. The destuctor deallocates

    /// this automatically allocated map, of course.

    ///

    /// \note The algorithm calls only the \ref lemon::Path::addFront()

    /// "addFront()" method of the given \ref lemon::Path "Path"

    /// structure.

    ///

    /// \return \c (*this)

    MinMeanCycle& cyclePath(Path &path) {

      if (local_path) {

	delete cycle_path;

	local_path = false;

      }

      cycle_path = &path;

      return *this;

    }

  }; //class MinMeanCycle

  ///@}

} //namespace lemon

#endif //LEMON_MIN_MEAN_CYCLE_H