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	SetDistMap
	Named parameter for setting `DistMap` type. More...

struct	SetPredMap
	Named parameter for setting `PredMap` type. More...

struct	SetProcessedMap
	Named parameter for setting `ProcessedMap` type. More...

struct	SetReachedMap
	Named parameter for setting `ReachedMap` type. More...

struct	SetStandardProcessedMap
	Named parameter for setting `ProcessedMap` type to be `Digraph::NodeMap<bool>`. 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 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.
void	init ()

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 ( const Digraph & g )

inline

Constructor.

Parameters

g	The digraph the algorithm runs on.

Member Function Documentation

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)

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)

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)

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)

void init ( )

inline

Initializes the internal data structures.

void addSource ( Node s )

inline

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

Node processNextNode ( )

inline

Processes the next node.

Returns: The processed node.

Precondition: The queue must not be empty.

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.

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.

Node nextNode ( ) const

inline

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

bool emptyQueue ( ) const

inline

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

int queueSize ( ) const

inline

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

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();

}

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);

}

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;

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();

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);

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 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.

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.

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.

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.

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.

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.

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.

Detailed Description

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

Classes

Public Types

Public Member Functions

Constructor & Destructor Documentation

Member Function Documentation

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