Heap< PR, IM, CMP > Class Template Reference

Detailed Description

template<typename PR, typename IM, typename CMP>
class lemon::concepts::Heap< PR, IM, CMP >

This concept class describes the main interface of heaps. The various heap structures are efficient implementations of the abstract data type priority queue. They store items with specified values called priorities in such a way that finding and removing the item with minimum priority are efficient. The basic operations are adding and erasing items, changing the priority of an item, etc.

Heaps are crucial in several algorithms, such as Dijkstra and Prim. Any class that conforms to this concept can be used easily in such algorithms.

Template Parameters

PR	Type of the priorities of the items.
IM	A read-writable item map with int values, used internally to handle the cross references.
CMP	A functor class for comparing the priorities. The default is std::less<PR>.

#include <lemon/concepts/heap.h>

Public Types
enum	State { IN_HEAP = 0, PRE_HEAP = -1, POST_HEAP = -2 }
	Type to represent the states of the items. More...
typedef IM	ItemIntMap
	Type of the item-int map.
typedef PR	Prio
	Type of the priorities.
typedef ItemIntMap::Key	Item
	Type of the items stored in the heap.

Public Member Functions
	Heap (ItemIntMap &map)
	Constructor.
	Heap (ItemIntMap &map, const CMP &comp)
	Constructor.
int	size () const
	The number of items stored in the heap.
bool	empty () const
	Check if the heap is empty.
void	clear ()
	Make the heap empty.
void	push (const Item &i, const Prio &p)
	Insert an item into the heap with the given priority.
Item	top () const
	Return the item having minimum priority.
Prio	prio () const
	The minimum priority.
void	pop ()
	Remove the item having minimum priority.
void	erase (const Item &i)
	Remove the given item from the heap.
Prio	operator[] (const Item &i) const
	The priority of the given item.
void	set (const Item &i, const Prio &p)
	Set the priority of an item or insert it, if it is not stored in the heap.
void	decrease (const Item &i, const Prio &p)
	Decrease the priority of an item to the given value.
void	increase (const Item &i, const Prio &p)
	Increase the priority of an item to the given value.
State	state (const Item &i) const
	Return the state of an item.
void	state (const Item &i, State st)
	Set the state of an item in the heap.

Member Enumeration Documentation

enum State

Each item has a state associated to it. It can be "in heap", "pre-heap" or "post-heap". The latter two are indifferent from the heap's point of view, but may be useful to the user.

The item-int map must be initialized in such way that it assigns PRE_HEAP (-1) to any element to be put in the heap.

Enumerator:

IN_HEAP	= 0. The "in heap" state constant.
PRE_HEAP	= -1. The "pre-heap" state constant.
POST_HEAP	= -2. The "post-heap" state constant.

Constructor & Destructor Documentation

Heap ( ItemIntMap &  map )

inlineexplicit

Constructor.

Parameters

map	A map that assigns int values to keys of type Item. It is used internally by the heap implementations to handle the cross references. The assigned value must be PRE_HEAP (-1) for each item.

Heap ( ItemIntMap &  map, const CMP &  comp  )

inlineexplicit

Constructor.

Parameters

map	A map that assigns int values to keys of type Item. It is used internally by the heap implementations to handle the cross references. The assigned value must be PRE_HEAP (-1) for each item.
comp	The function object used for comparing the priorities.

Member Function Documentation

int size ( ) const

inline

This function returns the number of items stored in the heap.

bool empty ( ) const

inline

This function returns true if the heap is empty.

void clear ( )

inline

This functon makes the heap empty. It does not change the cross reference map. If you want to reuse a heap that is not surely empty, you should first clear it and then you should set the cross reference map to PRE_HEAP for each item.

void push ( const Item &  i, const Prio &  p  )

inline

This function inserts the given item into the heap with the given priority.

Parameters

i	The item to insert.
p	The priority of the item.

Precondition

i must not be stored in the heap.

Item top ( ) const

inline

This function returns the item having minimum priority.

Precondition

The heap must be non-empty.

Prio prio ( ) const

inline

This function returns the minimum priority.

Precondition

The heap must be non-empty.

void pop ( )

inline

This function removes the item having minimum priority.

Precondition

The heap must be non-empty.

void erase ( const Item &  i )

inline

This function removes the given item from the heap if it is already stored.

Parameters

i	The item to delete.

Precondition

i must be in the heap.

Prio operator[] ( const Item &  i ) const

inline

This function returns the priority of the given item.

Parameters

i

The item.

Precondition

i must be in the heap.

void set ( const Item &  i, const Prio &  p  )

inline

This method sets the priority of the given item if it is already stored in the heap. Otherwise it inserts the given item into the heap with the given priority.

Parameters

i	The item.
p	The priority.

void decrease ( const Item &  i, const Prio &  p  )

inline

This function decreases the priority of an item to the given value.

Parameters

i	The item.
p	The priority.

Precondition

i must be stored in the heap with priority at least p.

void increase ( const Item &  i, const Prio &  p  )

inline

This function increases the priority of an item to the given value.

Parameters

i	The item.
p	The priority.

Precondition

i must be stored in the heap with priority at most p.

State state ( const Item &  i ) const

inline

This method returns PRE_HEAP if the given item has never been in the heap, IN_HEAP if it is in the heap at the moment, and POST_HEAP otherwise. In the latter case it is possible that the item will get back to the heap again.

Parameters

i

The item.

void state ( const Item &  i, State  st  )

inline

This function sets the state of the given item in the heap. It can be used to manually clear the heap when it is important to achive better time complexity.

Parameters

i	The item.
st	The state. It should not be IN_HEAP.