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 elements 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.

SEE ALSO

       Heap::Elem(3), Heap::Binary(3), Heap::Binomial(3), Heap::Fibonacci(3).