Bfs< GR, TR > Class Template Reference

Detailed Description

template<typename GR, typename TR>
class lemon::Bfs< GR, TR >

This class provides an efficient implementation of the BFS algorithm.

There is also a function-type interface for the BFS algorithm, which is convenient in the simplier cases and it can be used easier.

Template Parameters

GR	The type of the digraph the algorithm runs on. The default type is ListDigraph.
TR	The traits class that defines various types used by the algorithm. By default, it is BfsDefaultTraits<GR>. In most cases, this parameter should not be set directly, consider to use the named template parameters instead.

#include <lemon/bfs.h>

Classes
struct	SetPredMap
	Named parameter for setting More...
struct	SetDistMap
	Named parameter for setting More...
struct	SetReachedMap
	Named parameter for setting More...
struct	SetProcessedMap
	Named parameter for setting More...
struct	SetStandardProcessedMap
	Named parameter for setting More...

Public Types
typedef TR::Digraph	Digraph
	The type of the digraph the algorithm runs on.
typedef TR::PredMap	PredMap
	The type of the map that stores the predecessor arcs of the shortest paths.
typedef TR::DistMap	DistMap
	The type of the map that stores the distances of the nodes.
typedef TR::ReachedMap	ReachedMap
	The type of the map that indicates which nodes are reached.
typedef TR::ProcessedMap	ProcessedMap
	The type of the map that indicates which nodes are processed.
typedef PredMapPath< Digraph, PredMap >	Path
	The type of the paths.
typedef TR	Traits
	The traits class of the algorithm.

Public Member Functions
	Bfs (const Digraph &g)
	Constructor.
	~Bfs ()
	Destructor.
Bfs &	predMap (PredMap &m)
	Sets the map that stores the predecessor arcs.
Bfs &	reachedMap (ReachedMap &m)
	Sets the map that indicates which nodes are reached.
Bfs &	processedMap (ProcessedMap &m)
	Sets the map that indicates which nodes are processed.
Bfs &	distMap (DistMap &m)
	Sets the map that stores the distances of the nodes.
Execution Control
The simplest way to execute the BFS algorithm is to use one of the member functions called run(). If you need better control on the execution, you have to call
void	init ()
	Initializes the internal data structures.
void	addSource (Node s)
	Adds a new source node.
Node	processNextNode ()
	Processes the next node.
Node	processNextNode (Node target, bool &reach)
	Processes the next node.
template<class NM>
Node	processNextNode (const NM &nm, Node &rnode)
	Processes the next node.
Node	nextNode () const
	The next node to be processed.
bool	emptyQueue () const
	Returns false if there are nodes to be processed.
int	queueSize () const
	Returns the number of the nodes to be processed.
void	start ()
	Executes the algorithm.
void	start (Node t)
	Executes the algorithm until the given target node is reached.
template<class NodeBoolMap>
Node	start (const NodeBoolMap &nm)
	Executes the algorithm until a condition is met.
void	run (Node s)
	Runs the algorithm from the given source node.
bool	run (Node s, Node t)
	Finds the shortest path between s and t.
void	run ()
	Runs the algorithm to visit all nodes in the digraph.
Query Functions
The results of the BFS algorithm can be obtained using these functions. Either run() or start() should be called before using them.
Path	path (Node t) const
	The shortest path to the given node.
int	dist (Node v) const
	The distance of the given node from the root(s).
Arc	predArc (Node v) const
	Returns the 'previous arc' of the shortest path tree for the given node.
Node	predNode (Node v) const
	Returns the 'previous node' of the shortest path tree for the given node.
const DistMap &	distMap () const
	Returns a const reference to the node map that stores the distances of the nodes.
const PredMap &	predMap () const
	Returns a const reference to the node map that stores the predecessor arcs.
bool	reached (Node v) const
	Checks if the given node is reached from the root(s).

Constructor & Destructor Documentation

Bfs()

template<typename GR, typename TR>

Bfs ( const Digraph & g )

inline

Constructor.

Parameters

g	The digraph the algorithm runs on.

Member Function Documentation

predMap() [1/2]

template<typename GR, typename TR>

Bfs & predMap ( PredMap & m )

inline

Sets the map that stores the predecessor arcs. If you don't use this function before calling run() or init(), an instance will be allocated automatically. The destructor deallocates this automatically allocated map, of course.

Returns

(*this)

reachedMap()

template<typename GR, typename TR>

Bfs & reachedMap ( ReachedMap & m )

inline

Sets the map that indicates which nodes are reached. If you don't use this function before calling run() or init(), an instance will be allocated automatically. The destructor deallocates this automatically allocated map, of course.

Returns

(*this)

processedMap()

template<typename GR, typename TR>

Bfs & processedMap ( ProcessedMap & m )

inline

Sets the map that indicates which nodes are processed. If you don't use this function before calling run() or init(), an instance will be allocated automatically. The destructor deallocates this automatically allocated map, of course.

Returns

(*this)

distMap() [1/2]

template<typename GR, typename TR>

Bfs & distMap ( DistMap & m )

inline

Sets the map that stores the distances of the nodes calculated by the algorithm. If you don't use this function before calling run() or init(), an instance will be allocated automatically. The destructor deallocates this automatically allocated map, of course.

Returns

(*this)

init()

template<typename GR, typename TR>

void init ( )

inline

init() first, then you can add several source nodes with addSource(). Finally the actual path computation can be performed with one of the start() functions.

Initializes the internal data structures.

addSource()

template<typename GR, typename TR>

void addSource ( Node s )

inline

Adds a new source node to the set of nodes to be processed.

processNextNode() [1/3]

template<typename GR, typename TR>

Node processNextNode ( )

inline

Processes the next node.

Returns

The processed node.

Precondition

The queue must not be empty.

processNextNode() [2/3]

template<typename GR, typename TR>

Node processNextNode ( Node target, bool & reach )

inline

Processes the next node and checks if the given target node is reached. If the target node is reachable from the processed node, then the reach parameter will be set to true.

Parameters

target

The target node.

Return values

reach

Indicates if the target node is reached. It should be initially false.

Returns

The processed node.

Precondition

The queue must not be empty.

processNextNode() [3/3]

template<typename GR, typename TR>

template<class NM>

Node processNextNode ( const NM & nm, Node & rnode )

inline

Processes the next node and checks if at least one of reached nodes has true value in the nm node map. If one node with true value is reachable from the processed node, then the rnode parameter will be set to the first of such nodes.

Parameters

nm	A bool (or convertible) node map that indicates the possible targets.

Return values

rnode

The reached target node. It should be initially INVALID.

Returns

The processed node.

Precondition

The queue must not be empty.

nextNode()

template<typename GR, typename TR>

Node nextNode ( ) const

inline

Returns the next node to be processed or INVALID if the queue is empty.

emptyQueue()

template<typename GR, typename TR>

bool emptyQueue ( ) const

inline

Returns false if there are nodes to be processed in the queue.

queueSize()

template<typename GR, typename TR>

int queueSize ( ) const

inline

Returns the number of the nodes to be processed in the queue.

start() [1/3]

template<typename GR, typename TR>

void start ( )

inline

Executes the algorithm.

This method runs the BFS algorithm from the root node(s) in order to compute the shortest path to each node.

The algorithm computes

• the shortest path tree (forest),
• the distance of each node from the root(s).

  Precondition

  init() must be called and at least one root node should be added with addSource() before using this function.

  Note

  b.start() is just a shortcut of the following code.

  while ( !b.emptyQueue() ) {
    b.processNextNode();
  }

start() [2/3]

template<typename GR, typename TR>

void start ( Node t )

inline

Executes the algorithm until the given target node is reached.

This method runs the BFS algorithm from the root node(s) in order to compute the shortest path to t.

The algorithm computes

• the shortest path to t,
• the distance of t from the root(s).

  Precondition

  init() must be called and at least one root node should be added with addSource() before using this function.

  Note

  b.start(t) is just a shortcut of the following code.

  bool reach = false;
  while ( !b.emptyQueue() && !reach ) {
    b.processNextNode(t, reach);
  }

start() [3/3]

template<typename GR, typename TR>

template<class NodeBoolMap>

Node start ( const NodeBoolMap & nm )

inline

Executes the algorithm until a condition is met.

This method runs the BFS algorithm from the root node(s) in order to compute the shortest path to a node v with nm[v] true, if such a node can be found.

Parameters

nm	A bool (or convertible) node map. The algorithm will stop when it reaches a node v with nm[v] true.

Returns

The reached node v with nm[v] true or INVALID if no such node was found.

Precondition

init() must be called and at least one root node should be added with addSource() before using this function.

Note

b.start(nm) is just a shortcut of the following code.

Node rnode = INVALID;
while ( !b.emptyQueue() && rnode == INVALID ) {
  b.processNextNode(nm, rnode);
}
return rnode;

run() [1/3]

template<typename GR, typename TR>

void run ( Node s )

inline

This method runs the BFS algorithm from node s in order to compute the shortest path to each node.

The algorithm computes

• the shortest path tree,
• the distance of each node from the root.

  Note

  b.run(s) is just a shortcut of the following code.

  b.init();
  b.addSource(s);
  b.start();

run() [2/3]

template<typename GR, typename TR>

bool run ( Node s, Node t )

inline

This method runs the BFS algorithm from node s in order to compute the shortest path to node t (it stops searching when t is processed).

Returns

true if t is reachable form s.

Note

Apart from the return value, b.run(s,t) is just a shortcut of the following code.

b.init();
b.addSource(s);
b.start(t);

run() [3/3]

template<typename GR, typename TR>

void run ( )

inline

This method runs the BFS algorithm in order to visit all nodes in the digraph.

Note

b.run(s) is just a shortcut of the following code.

b.init();
for (NodeIt n(gr); n != INVALID; ++n) {
  if (!b.reached(n)) {
    b.addSource(n);
    b.start();
  }
}

path()

template<typename GR, typename TR>

Path path ( Node t ) const

inline

Returns the shortest path to the given node from the root(s).

Warning

t should be reached from the root(s).

Precondition

Either run() or init() must be called before using this function.

dist()

template<typename GR, typename TR>

int dist ( Node v ) const

inline

Returns the distance of the given node from the root(s).

Warning

If node v is not reached from the root(s), then the return value of this function is undefined.

Precondition

Either run() or init() must be called before using this function.

predArc()

template<typename GR, typename TR>

Arc predArc ( Node v ) const

inline

This function returns the 'previous arc' of the shortest path tree for the node v, i.e. it returns the last arc of a shortest path from a root to v. It is INVALID if v is not reached from the root(s) or if v is a root.

The shortest path tree used here is equal to the shortest path tree used in predNode() and predMap().

Precondition

Either run() or init() must be called before using this function.

predNode()

template<typename GR, typename TR>

Node predNode ( Node v ) const

inline

This function returns the 'previous node' of the shortest path tree for the node v, i.e. it returns the last but one node of a shortest path from a root to v. It is INVALID if v is not reached from the root(s) or if v is a root.

The shortest path tree used here is equal to the shortest path tree used in predArc() and predMap().

Precondition

Either run() or init() must be called before using this function.

distMap() [2/2]

template<typename GR, typename TR>

const DistMap & distMap ( ) const

inline

Returns a const reference to the node map that stores the distances of the nodes calculated by the algorithm.

Precondition

Either run() or init() must be called before using this function.

predMap() [2/2]

template<typename GR, typename TR>

const PredMap & predMap ( ) const

inline

Returns a const reference to the node map that stores the predecessor arcs, which form the shortest path tree (forest).

Precondition

Either run() or init() must be called before using this function.

reached()

template<typename GR, typename TR>

bool reached ( Node v ) const

inline

Returns true if v is reached from the root(s).

Precondition

Either run() or init() must be called before using this function.