Heap< PR, IM, Comp > Class Template Reference

Detailed Description

template<typename PR, typename IM, typename Comp = std::less<PR>>
class lemon::concepts::Heap< PR, IM, Comp >

Concept class describing the main interface of heaps. A heap is a data structure for storing items with specified values called priorities in such a way that finding the item with minimum priority is efficient. In a heap one can change the priority of an item, add or erase an item, etc.

Template Parameters

PR	Type of the priority of the items.
IM	A read and writable item map with int values, used internally to handle the cross references.
Comp	A functor class for the ordering of 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)
	The constructor.
int	size () const
	The number of items stored in the heap.
bool	empty () const
	Checks if the heap is empty.
void	clear ()
void	push (const Item &i, const Prio &p)
	Inserts an item into the heap with the given priority.
Item	top () const
	Returns the item having minimum priority.
Prio	prio () const
	The minimum priority.
void	pop ()
	Removes the item having minimum priority.
void	erase (const Item &i)
	Removes an item from the heap.
Prio	operator[] (const Item &i) const
	The priority of an item.
void	set (const Item &i, const Prio &p)
	Sets the priority of an item or inserts it, if it is not stored in the heap.
void	decrease (const Item &i, const Prio &p)
	Decreases the priority of an item to the given value.
void	increase (const Item &i, const Prio &p)
	Increases the priority of an item to the given value.
State	state (const Item &i) const
	Returns if an item is in, has already been in, or has never been in the heap.
void	state (const Item &i, State st)
	Sets 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 later two are indifferent from the point of view of the heap, but may be useful for 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

The 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 every item.

Member Function Documentation

int size ( ) const

inline

Returns the number of items stored in the heap.

bool empty ( ) const

inline

Returns true if the heap is empty.

void clear

(

)

Makes the heap empty.

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

inline

Inserts the given item into the heap with the given priority.

Parameters

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

Item top ( ) const

inline

Returns the item having minimum priority.

Precondition

The heap must be non-empty.

Prio prio ( ) const

inline

Returns the minimum priority.

Precondition

The heap must be non-empty.

void pop ( )

inline

Removes the item having minimum priority.

Precondition

The heap must be non-empty.

void erase ( const Item &  i )

inline

Removes the given item from the heap if it is already stored.

Parameters

i	The item to delete.

Prio operator[] ( const Item &  i ) const

inline

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 with the given priority.

Parameters

i	The item.
p	The priority.

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

inline

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

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

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 the better time complexity.

Parameters

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