BfsVisit< GR, VS, TR > Class Template Reference

Detailed Description

template<typename GR, typename VS, typename TR>
class lemon::BfsVisit< GR, VS, TR >

This class provides an efficient implementation of the BFS algorithm with visitor interface.

The BfsVisit class provides an alternative interface to the Bfs class. It works with callback mechanism, the BfsVisit object calls the member functions of the Visitor class on every BFS event.

This interface of the BFS algorithm should be used in special cases when extra actions have to be performed in connection with certain events of the BFS algorithm. Otherwise consider to use Bfs or bfs() instead.

Template Parameters

GR	The type of the digraph the algorithm runs on. The default type is ListDigraph. The value of GR is not used directly by BfsVisit, it is only passed to BfsVisitDefaultTraits.
VS	The Visitor type that is used by the algorithm. BfsVisitor<GR> is an empty visitor, which does not observe the BFS events. If you want to observe the BFS events, you should implement your own visitor class.
TR	The traits class that defines various types used by the algorithm. By default, it is BfsVisitDefaultTraits<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	SetReachedMap

Public Types
typedef TR	Traits
	The traits class.
typedef Traits::Digraph	Digraph
	The type of the digraph the algorithm runs on.
typedef VS	Visitor
	The visitor type used by the algorithm.
typedef Traits::ReachedMap	ReachedMap
	The type of the map that indicates which nodes are reached.

Public Member Functions
	BfsVisit (const Digraph &digraph, Visitor &visitor)
	Constructor.
	~BfsVisit ()
	Destructor.
BfsVisit &	reachedMap (ReachedMap &m)
	Sets the map that indicates which nodes are reached.
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<typename 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<typename NM >
Node	start (const NM &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.
bool	reached (Node v) const
	Checks if the given node is reached from the root(s).

Constructor & Destructor Documentation

BfsVisit ( const Digraph &  digraph, Visitor &  visitor  )

inline

Constructor.

Parameters

digraph	The digraph the algorithm runs on.
visitor	The visitor object of the algorithm.

Member Function Documentation

BfsVisit& 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)

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 NM &  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	must be 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();
  }
}

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.