Heap::Elem(3pm)

1Heap::Elem(3)         User Contributed Perl Documentation        Heap::Elem(3)
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NAME

6       Heap::Elem - Base class for elements in a Heap
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SYNOPSIS

9         use Heap::Elem::SomeInheritor;
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11         use Heap::SomeHeapClass;
12
13         $elem = Heap::Elem::SomeInheritor->new( $value );
14         $heap = Heap::SomeHeapClass->new;
15
16         $heap->add($elem);
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DESCRIPTION

19       This is an inheritable class for Heap Elements.  It provides the
20       interface documentation and some inheritable methods.  Only a child
21       classes can be used - this class is not complete.
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METHODS

24       $elem = Heap::Elem::SomeInheritor->new( [args] );
25           Creates a new Elem.  If there is exactly one arg, the Elem's value
26           will be set to that value.  If there is more than one arg provided,
27           the Elem's value will be set to an anonymous hash initialized to
28           the provided args (which must have an even number, of course).
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30       $elem->heap( $val ); $elem->heap;
31           Provides a method for use by the Heap processing routines.  If a
32           value argument is provided, it will be saved.  The new saved value
33           is always returned.  If no value argument is provided, the old
34           saved value is returned.
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36           The Heap processing routines use this method to map an element into
37           its internal structure.  This is needed to support the Heap methods
38           that affect elements that are not are the top of the heap -
39           decrease_key and delete.
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41           The Heap processing routines will ensure that this value is undef
42           when this elem is removed from a heap, and is not undef after it is
43           inserted into a heap.  This means that you can check whether an
44           element is currently contained within a heap or not.  (It cannot be
45           used to determine which heap an element is contained in, if you
46           have multiple heaps.  Keeping that information accurate would make
47           the operation of merging two heaps into a single one take longer -
48           it would have to traverse all of the elements in the merged heap to
49           update them; for Binomial and Fibonacci heaps that would turn an
50           O(1) operation into an O(n) one.)
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52       $elem->val( $val ); $elem->val;
53           Provides a method to get and/or set the value of the element.
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55       $elem1->cmp($elem2)
56           A routine to compare two elements.  It must return a negative value
57           if this element should go higher on the heap than $elem2, 0 if they
58           are equal, or a positive value if this element should go lower on
59           the heap than $elem2.  Just as with sort, the Perl operators <=>
60           and cmp cause the smaller value to be returned first; similarly you
61           can negate the meaning to reverse the order - causing the heap to
62           always return the largest element instead of the smallest.
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INHERITING

65       This class can be inherited to provide an object with the ability to be
66       heaped.  If the object is implemented as a hash, and if it can deal
67       with a key of heap, leaving it unchanged for use by the heap routines,
68       then the following implemetation will work.
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70         package myObject;
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72         require Exporter;
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74         @ISA = qw(Heap::Elem);
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76         sub new {
77             my $self = shift;
78             my $class = ref($self) || $self;
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80             my $self = SUPER::new($class);
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82             # set $self->{key} = $value;
83         }
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85         sub cmp {
86             my $self = shift;
87             my $other = shift;
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89             $self->{key} cmp $other->{key};
90         }
91
92         # other methods for the rest of myObject's functionality
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AUTHOR

95       John Macdonald, john@perlwolf.com
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COPYRIGHT

98       Copyright 1998-2007, O'Reilly & Associates.
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100       This code is distributed under the same copyright terms as perl itself.
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