/* -*- 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 algorithm for finding a minimum mean cycle.

#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 cycle.
  ///
  /// The \ref lemon::MinMeanCycle "MinMeanCycle" implements Karp's 
  /// algorithm for finding a minimum mean cycle.
  ///
  /// \param Graph The directed graph type the algorithm runs on.
  /// \param LengthMap The type of the length (cost) map.
  ///
  /// \author Peter Kovacs

#ifdef DOXYGEN
  template <typename Graph, typename LengthMap>
#else
  template <typename Graph,
    typename LengthMap = typename Graph::template EdgeMap<int> >
#endif

  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::InEdgeIt InEdgeIt;
    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;
    typedef typename NodeVector::iterator NodeVectorIt;

  protected:
  
    /// \brief Data sturcture 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> > PathVectorNodeMap;
  
  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.
    PathVectorNodeMap 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 The found cycle.
    Path *cycle_path;
    /// \brief 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), 
      cycle_length(0), cycle_size(-1), comp(_graph),
      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.
    void init() {
      comp_num = stronglyConnectedComponents(graph, comp);
      if (!cycle_path) {
	local_path = true;
	cycle_path = new Path;
      }
    }

    /// \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 (NodeVectorIt vi = nodes.begin(); vi != nodes.end(); ++vi) {
	dmap[*vi].resize(n + 1);
      }
    }
    
    /// \brief Processes all rounds of computing required path data.
    void processRounds() {
      dmap[nodes[0]][0] = PathData(true, 0);
      process.clear();
      for (OutEdgeIt oe(graph, nodes[0]); oe != INVALID; ++oe) {
	Node v = graph.target(oe);
	if (comp[v] != comp_cnt || v == nodes[0]) continue;
	dmap[v][1] = PathData(true, length[oe], oe);
	process.push_back(v);
      }
      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 (NodeVectorIt ui = process.begin(); ui != process.end(); ++ui) {
	for (OutEdgeIt oe(graph, *ui); oe != INVALID; ++oe) {
	  Node v = graph.target(oe);
	  if (comp[v] != comp_cnt) continue;
	  if ( !dmap[v][k].found || (dmap[v][k].dist > dmap[*ui][k-1].dist + length[oe]) ) {
	    if (!dmap[v][k].found) next.push_back(v); 
	    dmap[v][k] = PathData(true, dmap[*ui][k-1].dist + length[oe], oe);
	  }
	}
      }
      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 (NodeVectorIt ui = nodes.begin(); ui != nodes.end(); ++ui) {
	for (OutEdgeIt oe(graph, *ui); oe != INVALID; ++oe) {
	  Node v = graph.target(oe);
	  if (comp[v] != comp_cnt) continue;
	  if ( !dmap[v][k].found || (dmap[v][k].dist > dmap[*ui][k-1].dist + length[oe]) ) {
	    dmap[v][k] = PathData(true, dmap[*ui][k-1].dist + length[oe], oe);
	  }
	}
      }
    }
    
    /// \brief Finds the minimum cycle mean value according to the path
    /// data stored in \ref dmap.
    ///
    /// Finds the minimum cycle mean value according to the path data
    /// stored in \ref dmap.
    ///
    /// \retval min_length The total length of the found cycle.
    /// \retval min_size The number of edges in the found cycle.
    /// \retval min_node A node for obtaining a critical cycle.
    ///
    /// \return \c true if a cycle exists in the graph.
    bool findMinCycleMean(Length &min_length, int &min_size, Node &min_node) {
      bool found_min = false;
      for (NodeVectorIt vi = nodes.begin(); vi != nodes.end(); ++vi) {
	Length len;
	int size;
	bool found_one = false;
	int n = nodes.size();
	for (int k = 0; k < n; ++k) {
	  Length _len = dmap[*vi][n].dist - dmap[*vi][k].dist;
	  int _size = n - k; 
	  if ( dmap[*vi][n].found && dmap[*vi][k].found && (!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 = *vi;
	}
      }
      return found_min;
    }
    
    /// \brief Finds a critical (minimum mean) cycle according to the
    /// path data stored in \ref dmap.
    void findCycle(const Node &min_n) {
      IntNodeMap reached(graph, -1);
      int r = reached[min_n] = dmap[min_n].size() - 1;
      Node u = graph.source(dmap[min_n][r].pred);
      while (reached[u] < 0) {
	reached[u] = --r;
	u = graph.source(dmap[u][r].pred);
      }
      r = reached[u];
      Edge ce = dmap[u][r].pred;
      cycle_path->addFront(ce);
      Node v;
      while ((v = graph.source(ce)) != u) {
	ce = dmap[v][--r].pred;
	cycle_path->addFront(ce);
      }
    }
    
  public:

    /// \brief Runs the algorithm.
    ///
    /// Runs the algorithm.
    ///
    /// \return \c true if a cycle exists in the graph.
    bool run() {
      init();
      // Searching for the minimum mean cycle in all components
      bool found_cycle = false;
      Node cycle_node;
      for (comp_cnt = 0; comp_cnt < comp_num; ++comp_cnt) {
      
	initCurrent();
	processRounds();
	
	Length min_length;
	int min_size;
	Node min_node;
	bool found_min = findMinCycleMean(min_length, min_size, min_node);
	
	if ( found_min && (!found_cycle || min_length * cycle_size  < cycle_length * min_size) ) {
	  found_cycle = true;
	  cycle_length = min_length;
	  cycle_size = min_size;
	  cycle_node = min_node;
	}
      }
      if (found_cycle) findCycle(cycle_node);
      return found_cycle;
    }
    
    /// \brief Returns the total length of the found critical cycle.
    ///
    /// Returns the total length of the found critical cycle.
    ///
    /// \pre \ref run() must be called before using this function.
    Length cycleLength() const { 
      return cycle_length;
    }
    
    /// \brief Returns the number of edges in the found critical 
    /// cycle.
    ///
    /// Returns the number of edges in the found critical cycle.
    ///
    /// \pre \ref run() must be called before using this function.
    int cycleEdgeNum() const { 
      return cycle_size;
    }
    
    /// \brief Returns the mean length of the found critical cycle.
    ///
    /// Returns the mean length of the found critical cycle.
    ///
    /// \pre \ref run() must be called before using this function.
    ///
    /// \warning LengthMap::Value must be convertible to double.
    double minMean() const { 
      return (double)cycle_length / (double)cycle_size;
    }

    /// \brief Returns a const reference to the \ref lemon::Path "Path"
    /// structure of the found flow.
    ///
    /// Returns a const reference to the \ref lemon::Path "Path"
    /// structure of the found flow.
    ///
    /// \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