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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
PRType of the priorities of the items.
IMA read-writable item map with int values, used internally to handle the cross references.
CMPA 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
mapA 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
mapA 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.
compThe 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
iThe item to insert.
pThe 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
iThe 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
iThe 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
iThe item.
pThe priority.
void decrease ( const Item i,
const Prio p 
)
inline

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

Parameters
iThe item.
pThe 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
iThe item.
pThe 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
iThe 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
iThe item.
stThe state. It should not be IN_HEAP.