Heap::Elem(3) User Contributed Perl Documentation Heap::Elem(3)NAMEHeap::Elem - Base class for elements in a Heap
SYNOPSIS
use Heap::Elem::SomeInheritor;
use Heap::SomeHeapClass;
$elem = Heap::Elem::SomeInheritor->new( $value );
$heap = Heap::SomeHeapClass->new;
$heap->add($elem);
DESCRIPTION
This is an inheritable class for Heap Elements. It provides the
interface documentation and some inheritable methods. Only a child
classes can be used - this class is not complete.
METHODS
$elem = Heap::Elem::SomeInheritor->new( [args] );
Creates a new Elem. If there is exactly one arg, the Elem's value
will be set to that value. If there is more than one arg provided,
the Elem's value will be set to an anonymous hash initialized to
the provided args (which must have an even number, of course).
$elem->heap( $val ); $elem->heap;
Provides a method for use by the Heap processing routines. If a
value argument is provided, it will be saved. The new saved value
is always returned. If no value argument is provided, the old
saved value is returned.
The Heap processing routines use this method to map an element into
its internal structure. This is needed to support the Heap methods
that affect elements that are not are the top of the heap -
decrease_key and delete.
The Heap processing routines will ensure that this value is undef
when this elem is removed from a heap, and is not undef after it is
inserted into a heap. This means that you can check whether an
element is currently contained within a heap or not. (It cannot be
used to determine which heap an element is contained in, if you
have multiple heaps. Keeping that information accurate would make
the operation of merging two heaps into a single one take longer -
it would have to traverse all of the elements in the merged heap to
update them; for Binomial and Fibonacci heaps that would turn an
O(1) operation into an O(n) one.)
$elem->val( $val ); $elem->val;
Provides a method to get and/or set the value of the element.
$elem1->cmp($elem2)
A routine to compare two elements. It must return a negative value
if this element should go higher on the heap than $elem2, 0 if they
are equal, or a positive value if this element should go lower on
the heap than $elem2. Just as with sort, the Perl operators <=>
and cmp cause the smaller value to be returned first; similarly you
can negate the meaning to reverse the order - causing the heap to
always return the largest element instead of the smallest.
INHERITING
This class can be inherited to provide an object with the ability to be
heaped. If the object is implemented as a hash, and if it can deal
with a key of heap, leaving it unchanged for use by the heap routines,
then the following implemetation will work.
package myObject;
require Exporter;
@ISA = qw(Heap::Elem);
sub new {
my $self = shift;
my $class = ref($self) || $self;
my $self = SUPER::new($class);
# set $self->{key} = $value;
}
sub cmp {
my $self = shift;
my $other = shift;
$self->{key} cmp $other->{key};
}
# other methods for the rest of myObject's functionality
AUTHOR
John Macdonald, john@perlwolf.com
COPYRIGHT
Copyright 1998-2007, O'Reilly & Associates.
This code is distributed under the same copyright terms as perl itself.
SEE ALSOHeap(3), Heap::Elem::Num(3), Heap::Elem::NumRev(3), Heap::Elem::Str(3),
Heap::Elem::StrRev(3).
perl v5.18.2 2007-04-28 Heap::Elem(3)
