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.

#include <lemon/bfs.h>

List of all members.

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 more control on the execution, first you have to call init(), 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 a node.
int	dist (Node v) const
	The distance of a node from the root(s).
Arc	predArc (Node v) const
	Returns the 'previous arc' of the shortest path tree for a node.
Node	predNode (Node v) const
	Returns the 'previous node' of the shortest path tree for a 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 a node is reached from the root(s).

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Constructor & Destructor Documentation

Bfs

(

const Digraph &

g

)

[inline]

Constructor.

Parameters:

g	The digraph the algorithm runs on.

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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 compute the shortest path to each node.

The algorithm computes

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

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 a node.

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 a 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().

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 from 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().

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.

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.