NAME
Algorithm::Heapify::XS - Perl extension for supplying simple heap
primitives for arrays.
SYNOPSIS
use Algorithm::Heapify::XS qw(max_heapify max_heap_shift);
my @array= (1..10);
max_heapify(@array);
while (defined(my $top= max_heap_shift(@array))) {
print $top;
}
DESCRIPTION
A heap is an array based data structure where the array is treated as a
balanced tree of items where each item obeys a given inequality
constraint with its parent and children, but not with its siblings. This
allows it to be put into "nearly" sorted order more efficiently than an
actual sort would.
This data structure has a number of nice properties:
a) the tree does not require "child" pointers, but instead infers
parent/child relationships from their position in the array. The parent
of a node i is defined to reside in position int((i-1)/2), and the left
and right children of a node i reside in position (i*2+1) and (i*2+2)
respectively.
b) "heapifying" an array is O(N) as compared to N * log2(N) for a
typical sort.
c) Accessing the top item is O(1), and removing it from the array is
O(log(N)).
d) Inserting a new item into the heap is O(log(N))
This means that for applications that need find only the top K of an
array can do it faster than sorting the array, and there is no need for
wrapper objects to represent the tree.
INTERFACE
All operations are in-place on the array passed as an argument, and all
require that the appropriate "heapify" (either max_heapify or
min_heapify) operation has been called on the array first. Typically
they return the "top" of the heap after the operation has been
performed, with the exception of the "shift" operation which returns the
"top" of the heap before removing it.
There are four variants of all subs provided. The "max_" and "min_"
variants, and the "maxstr_" and "minstr_" which provide descending and
ascending and numeric and string ordering respectively. If you wish more
precise control over the ordering of items in the heap, such as objects,
then "use overload" to provide the required semantics by overloading the
appropriate inequality operators, typically just one of "<=>" or "cmp"
operators need be overloaded.
EXPORT
None by default. All exports must be requested, or you can use ":all" to
import then all, you can also import groups by prefix, eg ":max",
":min", ":maxstr", ":minstr" and ":idx" to export
SUBS
$max= max_heapify(@array)
$min= min_heapify(@array)
$maxstr= maxstr_heapify(@array)
$minstr= minstr_heapify(@array)
These subs "heapify" the array and return its "top" (min/max) value.
Prior use of the appropriate one of these subs is required to use
all the other subs offered by this package.
$max= max_heap_shift(@array)
$min= min_heap_shift(@array)
$maxstr= maxstr_heap_shift(@array)
$minstr= minstr_heap_shift(@array)
Return and remove the "top" (min/max) value from a heapified array
while maintain the arrays heap-order.
$max= max_heap_push(@array)
$min= min_heap_push(@array)
$maxstr= maxstr_heap_push(@array)
$minstr= minstr_heap_push(@array)
Insert an item into a heapified array while maintaining the arrays
heap-order, and return the resulting "top" (min/max) value.
$max= max_heap_adjust_top(@array)
$min= min_heap_adjust_top(@array)
$maxstr= maxstr_heap_adjust_top(@array)
$minstr= minstr_heap_adjust_top(@array)
If the weight of the top item in a heapified array ($array[0]) has
changed, this function will adjust its position in the tree, and
return the resulting new "top" (min/max) value.
$max= max_heap_adjust_item(@array,$idx)
$min= min_heap_adjust_item(@array,$idx)
$maxstr= maxstr_heap_adjust_item(@array,$idx)
$minstr= minstr_heap_adjust_item(@array,$idx)
If the weight of a specific item in a heapified array has changed,
this function will adjust its position in the tree, and return the
resulting new "top" (min/max) value. If $idx is outside the array
does nothing.
$idx= heap_parent_idx($idx)
Returns the defined location for the node residing at index $idx in
a heap, or undef if the $idx is 0.
$idx= heap_left_child_idx($idx)
$idx= heap_right_child_idx($idx)
Returns the defined location for the children of a node residing at
index $idx in a heap.
VERSION
This is version 0.04
INSTALLATION
To install this module type the following:
perl Makefile.PL
make
make test
make install
DEPENDENCIES
This module is implemented in XS, and requires a working C compiler and
Perl build tools environment to build.
SEE ALSO
CPAN - There are other heap packages with different interfaces if you
don't like this one.
AUTHOR
Yves Orton,
COPYRIGHT AND LICENSE
Copyright (C) 2018 by Yves Orton
This software is released under the "MIT License".
See the file LICENSE.txt for more specifics.