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NAME

       Heap - Perl extensions for keeping data partially sorted

SYNOPSIS

         use Heap;

         my $heap = Heap->new;
         my $elem;

         use Heap::Elem::Num(NumElem);

         foreach $i ( 1..100 ) {
             $elem = NumElem( $i );
             $heap->add( $elem );
         }

         while( defined( $elem = $heap->extract_top ) ) {
             print "Smallest is ", $elem->val, "\n";
         }

DESCRIPTION

       The Heap collection of modules provide routines that manage a heap of
       elements.  A heap is a partially sorted structure that is always able
       to easily extract the smallest of the elements in the structure (or the
       largest if a reversed compare routine is provided).

       If the collection of elements is changing dynamically, the heap has
       less overhead than keeping the collection fully sorted.

       The elements must be objects as described in "Heap::Elem" and all ele-
       ments inserted into one heap must be mutually compatible - either the
       same class exactly or else classes that differ only in ways unrelated
       to the Heap::Elem interface.

METHODS

       $heap = HeapClass::new(); $heap2 = $heap1->new();
           Returns a new heap object of the specified (sub-)class.  This is
           often used as a subroutine instead of a method, of course.

       $heap->DESTROY
           Ensures that no internal circular data references remain.  Some
           variants of Heap ignore this (they have no such references).  Heap
           users normally need not worry about it, DESTROY is automatically
           invoked when the heap reference goes out of scope.

       $heap->add($elem)
           Add an element to the heap.

       $elem = $heap->top
           Return the top element on the heap.  It is not removed from the
           heap but will remain at the top.  It will be the smallest element
           on the heap (unless a reversed cmp function is being used, in which
           case it will be the largest).  Returns undef if the heap is empty.

           This method used to be called "minimum" instead of "top".  The old
           name is still supported but is deprecated.  (It was confusing to
           use the method "minimum" to get the maximum value on the heap when
           a reversed cmp function was used for ordering elements.)

       $elem = $heap->extract_top
           Delete the top element from the heap and return it.  Returns undef
           if the heap was empty.

           This method used to be called "extract_minimum" instead of
           "extract_top".  The old name is still supported but is deprecated.
           (It was confusing to use the method "extract_minimum" to get the
           maximum value on the heap when a reversed cmp function was used for
           ordering elements.)

       $heap1->absorb($heap2)
           Merge all of the elements from $heap2 into $heap1.  This will leave
           $heap2 empty.

       $heap1->decrease_key($elem)
           The element will be moved closed to the top of the heap if it is
           now smaller than any higher parent elements.  The user must have
           changed the value of $elem before decrease_key is called.  Only a
           decrease is permitted.  (This is a decrease according to the cmp
           function - if it is a reversed order comparison, then you are only
           permitted to increase the value of the element.  To be pedantic,
           you may only use decrease_key if $elem-cmp($elem_original) <= 0> if
           $elem_original were an elem with the value that $elem had before it
           was decreased.)

       $elem = $heap->delete($elem)
           The element is removed from the heap (whether it is at the top or
           not).

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.

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