PairingHeap< PR, IM, CMP > Class Template Reference

Detailed Description

template<typename PR, typename IM, typename CMP>
class lemon::PairingHeap< PR, IM, CMP >

This class implements the pairing heap data structure. It fully conforms to the heap concept.

The methods increase() and erase() are not efficient in a pairing heap. In case of many calls of these operations, it is better to use other heap structure, e.g. binary heap.

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/pairing_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.
typedef CMP	Compare
	Functor type for comparing the priorities.

Public Member Functions
	PairingHeap (ItemIntMap &map)
	Constructor.
	PairingHeap (ItemIntMap &map, const Compare &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	set (const Item &item, const Prio &value)
	Set the priority of an item or insert it, if it is not stored in the heap.
void	push (const Item &item, const Prio &value)
	Insert an item into the heap with the given priority.
Item	top () const
	Return the item having minimum priority.
const Prio &	prio () const
	The minimum priority.
const Prio &	operator[] (const Item &item) const
	The priority of the given item.
void	pop ()
	Remove the item having minimum priority.
void	erase (const Item &item)
	Remove the given item from the heap.
void	decrease (Item item, const Prio &value)
	Decrease the priority of an item to the given value.
void	increase (Item item, const Prio &value)
	Increase the priority of an item to the given value.
State	state (const Item &item) 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

State

template<typename PR , typename IM , typename CMP >

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.
PRE_HEAP	= -1.
POST_HEAP	= -2.

Constructor & Destructor Documentation

PairingHeap() [1/2]

template<typename PR , typename IM , typename CMP >

PairingHeap ( ItemIntMap &  map )

inlineexplicit

Constructor.

Parameters

map	A map that assigns int values to the items. It is used internally to handle the cross references. The assigned value must be PRE_HEAP (-1) for each item.

PairingHeap() [2/2]

template<typename PR , typename IM , typename CMP >

PairingHeap ( ItemIntMap &  map, const Compare &  comp  )

inline

Constructor.

Parameters

map	A map that assigns int values to the items. It is used internally 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

size()

template<typename PR , typename IM , typename CMP >

int size ( ) const

inline

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

empty()

template<typename PR , typename IM , typename CMP >

bool empty ( ) const

inline

This function returns true if the heap is empty.

clear()

template<typename PR , typename IM , typename CMP >

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.

set()

template<typename PR , typename IM , typename CMP >

void set ( const Item &  item, const Prio &  value  )

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

item	The item.
value	The priority.

push()

template<typename PR , typename IM , typename CMP >

void push ( const Item &  item, const Prio &  value  )

inline

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

Parameters

item	The item to insert.
value	The priority of the item.

Precondition

item must not be stored in the heap.

top()

template<typename PR , typename IM , typename CMP >

Item top ( ) const

inline

This function returns the item having minimum priority.

Precondition

The heap must be non-empty.

prio()

template<typename PR , typename IM , typename CMP >

const Prio & prio ( ) const

inline

This function returns the minimum priority.

Precondition

The heap must be non-empty.

operator[]()

template<typename PR , typename IM , typename CMP >

const Prio & operator[] ( const Item &  item ) const

inline

This function returns the priority of the given item.

Parameters

item

The item.

Precondition

item must be in the heap.

pop()

template<typename PR , typename IM , typename CMP >

void pop ( )

inline

This function removes the item having minimum priority.

Precondition

The heap must be non-empty.

erase()

template<typename PR , typename IM , typename CMP >

void erase ( const Item &  item )

inline

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

Parameters

item	The item to delete.

Precondition

item must be in the heap.

decrease()

template<typename PR , typename IM , typename CMP >

void decrease ( Item  item, const Prio &  value  )

inline

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

Parameters

item	The item.
value	The priority.

Precondition

item must be stored in the heap with priority at least value.

increase()

template<typename PR , typename IM , typename CMP >

void increase ( Item  item, const Prio &  value  )

inline

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

Parameters

item	The item.
value	The priority.

Precondition

item must be stored in the heap with priority at most value.

state() [1/2]

template<typename PR , typename IM , typename CMP >

State state ( const Item &  item ) 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

item

The item.

state() [2/2]

template<typename PR , typename IM , typename CMP >

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.