File Coverage

blib/lib/Tree/AVL.pm

Criterion	Covered	Total	%
statement	293	581	50.4
branch	127	290	43.7
condition	17	36	47.2
subroutine	26	47	55.3
pod	14	40	35.0
total	477	994	47.9

##############################################################################
#
# AVL.pm
#
# An implementation of an AVL tree for storing comparable objects.
#
# AVL Trees are balanced binary trees, first introduced
# in "An Algorithm for the Organization of Data" by
# Adelson-Velskii and Landis in 1962.
#
# Balance is kept in an AVL tree during insertion and
# deletion by maintaining a 'balance' factor in each node.
#
# If the subtree below any node in the tree is evenly balanced,
# the balance factor for that node will be 0.
#
# When the right-subtree below a node is taller than the left-subtree,
# the balance factor will be 1.  For the opposite case, the balance
# factor will be -1.
#
# If the either subtree is heavier (taller by more than 2 levels) than the
# other, the balance factor within the node will be set to (+-)2,
# and the subtree below that node will be rebalanced.
#
# Re-balancing is done via 'single' or 'double' rotations, each of which
# takes constant-time.
#
# Insertion into an AVL tree will require at most 1 rotation.
#
# Deletion from an AVL tree may take as much as log(n) rotations
# in order to restore balance.
#
# Balanced trees can save huge amounts of time in your programs
# when used over regular flat data-structures.  For example, if
# you are processing as much as 1,125,899,906,842,624 ordered objects
# on some super awesome mega workstation, the worst-case time (comparisons)
# required  to access one of those objects will be on the order of
# ~1,125,899,906,842,624 (one quadrillion, one hundred twenty-five trillion,
# eight hundred eighty-nine billion, nine hundred six million, eight hundred
# forty-two thousand, six hundred twenty-four) if you keep them in a flat
# data structure.    However, using a balanced tree such as a 2-3 tree, a
# Red-Black tree or an AVL tree, the worst-case time (comparisons) required
# will be on the order of 50.
#
##############################################################################

package Tree::AVL;

use Carp;
use strict;
use warnings;

our $VERSION = '1.075';


##################################################
#
#  AVL tree constructor
#
##################################################
sub new {
    my $invocant = shift;
    my $class   = ref($invocant) || $invocant;
    my $self = {
	_node => {
	    _obj             => undef,   # Object to store in AVL tree
	    _left_node       => undef,
	    _right_node      => undef,
	    _height          => 0,
	    _balance         => 0,     # (abs(balance) < 2) <-> AVL property
	},

	fcompare         => undef,   # comparison function
	fget_key         => undef,   # function to get key from obj
	fget_data        => undef,  # function to get data from obj

	acc_lookup_hash  => undef,
        @_,    # Override previous attributes
    };

    $self = bless $self, $class;

    if(!$self->{fcompare}){
	$self->{fcompare}  = \&default_cmp_func;
    }
    if(!$self->{fget_key}){
	$self->{fget_key}  = sub{ return $_[0]; };
    }
    if(!$self->{fget_data}){
	$self->{fget_data}  = sub{ return $_[0]; };
    }

    return $self;
}


#
# insert
#
# usage:   $tree->insert($object);
#
sub insert
{
    my ($self, $object) = @_;
    if(!defined($object)){
	croak "Error: cannot insert uninitialized object into AVL tree.\n";
    }
    $self->avl_insert($object);
    return;
}


#
# avl_insert
#
# usage:  $tree_object->avl_insert($object);
#
sub avl_insert
{
    my ($self, $object, $node, $depth) = @_;

    if(!$depth){
	$depth = 0;
    }
    if(!$node){
	$node = \$self->{_node};
    }

    my $get_key_func = $self->{fget_key};
    my $key = $get_key_func->($object);

    my $node_obj = $$node->{_obj};
    my $own_key;

    my $increase = 0;
    my $change = 0;

    if( !defined($self->{_node}->{_obj}) ) # no root data yet, so populate with $object
    {
	$self->{_node}->{_obj} = $object;

	return;
    }
    else # need to insert object if object is not already in tree
    {
	$own_key = $node_obj->$get_key_func();
	if(!defined($own_key)){
	    croak "Error:  get_key() method provided to Tree::AVL object returned a null value\n";
	}

	my $cmpfunc = $self->{fcompare};
	my $result = $cmpfunc->($node_obj, $object);

	if($result == 0){ #element is already in tree, do nothing.
	    return 0;
	}
	elsif($result < 0){ # insert into right subtree
	    if (!defined($$node->{_right_node})){ # Need to create a new node.


		my $new_node = {
			_obj      => $object,
			_balance  => 0,
			_right_node => undef,
			_left_node => undef,
		};

		$$node->{_right_node} = $new_node;
		$increase = 1;
	    }
	    else{ # descend and insert into right subtree
		$change = $self->avl_insert($object, \$$node->{_right_node}, $depth+1);
		$increase = 1 * $change;
	    }
	}
	else{  # insert into left subtree
	    if (!defined($$node->{_left_node})){  # Need to create a new node.

		my $new_node = {
		    _obj      => $object,
		    _balance  => 0,
		    _right_node => undef,
		    _left_node => undef,
		};

		$$node->{_left_node} = $new_node;
		$increase = -1;
	    }
	    else{ # descend and insert into left subtree
		$change = $self->avl_insert($object, \$$node->{_left_node}, $depth+1);
		$increase = -1 * $change;
	    }
	}
    } # end else determine whether need to insert into left or right subtree

    $$node->{_balance} = $$node->{_balance} + $increase;

    if($increase && $$node->{_balance}){
	my $height_change = $self->rebalance($node);
	$change = 1 - $height_change;
    }
    else{
	$change = 0;
    }

    if($depth == 0){
	$self->{_node} = $$node;
    }

    return $change;
}


#
# remove
#
# usage:  my $found_obj = $avltree->remove($object);
#
# remove an object from tree.
#
#
sub remove
{
    my ($self, $object) = @_;
    my ($obj) = $self->delete($object);
    return $obj;
}


#
# avl_delete
#
# usage:  ($found_obj) = $tree->delete($object);
#
#
sub delete
{

    my ($self, $object, $node, $depth) = @_;

    if(!$node){
	$node = \$self->{_node};
    }
    if(!$depth){
	$depth = 0;
    }

    my $deleted_node;
    my $change = 0;
    my $decrease = 0;

    if(!defined($$node->{_obj})){ # no root data yet
  	return;
    }
    else{
	my $node_obj = $$node->{_obj};
	my $get_key_func = $self->{fget_key};
	my $own_key = $get_key_func->($node_obj);
	my $cmpfunc = $self->{fcompare};

	my $result = $cmpfunc->($node_obj, $object);
	if($result > 0){  # look into left subtree
	    if (!defined($$node->{_left_node})){
		return;
	    }
	    else{
		($deleted_node, my $new_ref, $change) = Tree::AVL::delete($self, $object, \$$node->{_left_node}, $depth+1);
		if($deleted_node){
		    $$node->{_left_node} = $new_ref;
		    $decrease = -1 * $change;
		}
		else{
		    return;
		}
	    }
	}
	elsif($result < 0){ # look into right subtree
	    if (!defined($$node->{_right_node})){
		return;
	    }
	    else{
		($deleted_node, my $new_ref, $change) = Tree::AVL::delete($self, $object, \$$node->{_right_node}, $depth+1);
		if($deleted_node){
		    $$node->{_right_node} = $new_ref;
		    $decrease = 1 * $change;
		}
		else{
		    return;
		}
	    }
	}
	elsif($result == 0){ # this the node we want to delete FOUND THE NODE.
	    $deleted_node = $$node->{_obj};

	    if(!$$node->{_left_node} && !$$node->{_right_node}){  # this is the node to delete, and it is a leaf node.

		if($depth == 0){ # this is also the root node.

		    $$node = {
			_obj      => undef,
			_balance  => 0,
			_right_node => undef,
			_left_node => undef,
		    };

		}
		else{
		    # this is the node to delete.  It is not the root node and it has no children (it is a leaf)
		    $$node = undef;

		    $change = 1;
		    return ($deleted_node, $$node, $change);
		}
	    }
	    elsif(!$$node->{_left_node}){
		$$node = $$node->{_right_node};
		$change = 1;

		return ($deleted_node, $$node, $change);
	    }
	    elsif(!$$node->{_right_node}){
		$$node = $$node->{_left_node};
		$change = 1;

		return ($deleted_node, $$node, $change);
	    }
	    elsif($$node->{_right_node} && $$node->{_left_node}){
		    (my $new_root_obj, $$node->{_right_node}, $change) = $self->delete_smallest(\$$node->{_right_node});
		    if($self->is_empty($$node->{_right_node})){
			delete $$node->{_right_node};
		    }
		    $$node->{_obj} = $new_root_obj;
	    }

	    $decrease = $change;

	}  # end else determine whether need to look into left or right subtree, or neither
    } # end else() there was root data.

    $$node->{_balance} = $$node->{_balance} - $decrease;
    if($decrease){
	if($$node->{_balance}){
	    $change = $self->rebalance($node);
	}
	else{
	    $change = 1;
	}
    }
    else{
	$change = 0;
    }

    return ($deleted_node, $$node, $change);
}


#
# delete_smallest
#
# usage:  $tree_object->delete_smallest();
#
sub delete_smallest
{
    my ($self,
	$node,
	$depth) = @_;

    if(!$node){
	$node = \$self->{_node};
    }

    my $node_obj = $$node->{_obj};
    my $get_key_func = $self->{fget_key};
    my $own_key = $get_key_func->($node_obj);
    my $decrease = 0;
    my $change = 0;

    if(!$$node->{_left_node}){
	my $obj = $$node->{_obj};
	if(!$$node->{_right_node} && !$depth){
	    $$node = {
		_obj      => undef,
		_balance  => 0,
		_right_node => undef,
		_left_node => undef,
	    };
	    $change = 1;
	}
	else{
	    if($$node->{_right_node}){
		$$node = $$node->{_right_node};
	    }
	    else{
		$$node = undef;
	    }
	    if($$node){
		$$node->{_balance} = 0;
	    }
	    $change = 1;
	}
	return ($obj, $$node, $change);
    }
    else{
	my ($obj, $newleft, $change) = Tree::AVL::delete_smallest($self, \$$node->{_left_node}, 1);
	$decrease = -1 * $change;
	$$node->{_left_node} = $newleft;
	$$node->{_balance} = $$node->{_balance} - $decrease;
	if($decrease){
	    if($$node->{_balance}){
		$change = $self->rebalance($node);
	    }
	    else{
		$change = 1;
	    }
	}
	return ($obj, $$node, $change);
    }
}


#
# delete_largest
#
# usage:  $tree_object->delete_largest();
#
sub delete_largest
{
    my ($self,
	$node,
	$depth) = @_;

    if(!$node){
	$node = \$self->{_node};
    }

    my $node_obj = $$node->{_obj};
    my $get_key_func = $self->{fget_key};
    my $own_key = $get_key_func->($node_obj);
    my $decrease = 0;
    my $change = 0;

    if(!$$node->{_right_node}){
	my $obj = $$node->{_obj};
	if(!$$node->{_left_node} && !$depth){
	    $$node = {
		_obj        => undef,
		_balance    => 0,
		_right_node => undef,
		_left_node  => undef,
	    };
	    $change = 1;
	}
	else{
	    if($$node->{_left_node}){
		$$node = $$node->{_left_node};
	    }
	    else{
		$$node = undef;
	    }
	    if($$node){
		$$node->{_balance} = 0;
	    }
	    $change = 1;
	}
	return ($obj, $$node, $change);
    }
    else{
	my ($obj, $newright, $change) = Tree::AVL::delete_largest($self, \$$node->{_right_node}, 1);
	$decrease = 1 * $change;
	$$node->{_right_node} = $newright;
	$$node->{_balance} = $$node->{_balance} - $decrease;
	if($decrease){
	    if($$node->{_balance}){
		$change = $self->rebalance($node);
	    }
	    else{
		$change = 1;
	    }
	}
	return ($obj, $$node, $change);
    }
}




#
# rebalance
#
# Determines what sort of, if any, imbalance exists in the subtree
# rooted at $node, and calls the correct rotation subroutine.
#
sub rebalance
{
    my ($self, $node) = @_;
    my $height_change = 0;

    if($$node->{_balance} < -1){  # left heavy
	if($$node->{_left_node}){
	    if($$node->{_left_node}->{_balance} == 1){ # right heavy
		$height_change = $self->double_rotate_right($node);
	    }
	    else{
		$height_change = $self->rotate_right($node);
	    }
	}
    }
    elsif($$node->{_balance} > 1){ # right heavy
	if($$node->{_right_node}){
	    if($$node->{_right_node}->{_balance} == -1){ # left heavy
		$height_change = $self->double_rotate_left($node);
	    }
	    else{
		$height_change = $self->rotate_left($node);
	    }
	}
    }
    return $height_change;
}



#
# rotate_right
#
# A single right-rotation.  Yes, this is *very* similar code for right and left operations,
# but these subroutines have not been merged to one in the interest of clarity.  After all, according to
# Abelson and Sussman, programs are for humans to read above all, and only incidentally for machines
# to run.   Not that this code is as readable as it could be, of course.
#
sub rotate_right
{
    my ($self, $node) = @_;
    my $height_change = 0;
    my $lr_grandchild;
    my $lnode;

    if($$node->{_left_node}){
	$lnode = $$node->{_left_node};
    }

    # determine height_change
    if($$node->{_right_node} && $$node->{_left_node}){
	$height_change = $$node->{_left_node}->{_balance} == 0 ? 0 : 1;
    }
    else{
	$height_change = 1;
    }

    # do the rotation
    if(defined($$node->{_left_node})){
	if($$node->{_left_node}->{_right_node}){
	    $lr_grandchild = $$node->{_left_node}->{_right_node}; # becomes left child's new right child
	}
    }
    $$node->{_left_node} = $lr_grandchild;
    if($lnode){
	$lnode->{_right_node} = $$node;
	$$node =  $lnode;
    }

    # update balances
    if($$node->{_right_node}){
	$$node->{_right_node}->{_balance} = $$node->{_right_node}->{_balance} + (1 - min($$node->{_balance}, 0));
	$$node->{_balance} = $$node->{_balance} + (1 + max($$node->{_right_node}->{_balance}, 0));
    }

    return $height_change;
}

#
# rotate_left
#
# A single left-rotation.  Yes, this is *very* similar code for right and left operations,
# but these subroutines have not been merged to one in the interest of clarity.  After all, according to
# Abelson and Sussman, programs are for humans to read above all, and only incidentally for machines
# to run.  Not that this code is as readable as it could be, of course.
#
sub rotate_left
{
    my ($self, $node) = @_;
    my $height_change = 0;
    my $rl_grandchild;
    my $rnode;

    if($$node->{_right_node}){
	$rnode = $$node->{_right_node};
    }

    # determine height_change
    if($$node->{_left_node} && $$node->{_right_node}){
	$height_change = $$node->{_right_node}->{_balance} == 0 ? 0 : 1;
    }
    else{
	$height_change = 1;
    }

    if(defined($$node->{_right_node})){
	if($$node->{_right_node}->{_left_node}){
	    $rl_grandchild = $$node->{_right_node}->{_left_node}; # becomes left child's new right child
	}
    }
    $$node->{_right_node} = $rl_grandchild;

    if($rnode){
	$rnode->{_left_node} = $$node;
	$$node =  $rnode;
    }

     # update balances
    if($$node->{_left_node}){
	$$node->{_left_node}->{_balance} = $$node->{_left_node}->{_balance} - (1 + max($$node->{_balance}, 0));
	$$node->{_balance} = $$node->{_balance} - (1 - min($$node->{_left_node}->{_balance}, 0));
    }

    return $height_change;
}


#
# double_rotate_right
#
# A double right-rotation.  Yes, this is *very* similar code for right and left operations,
# but these subroutines have not been merged to one in the interest of clarity.  After all, according to
# Abelson and Sussman, programs are for humans to read above all, and only incidentally for machines
# to run.  Not that this code is as readable as it could be, of course.
#
sub double_rotate_right
{
    my ($self, $node) = @_;

    my $old_balance = $$node->{_balance};
    my $old_l_balance = 0;
    my $old_r_balance = 0;

    if($$node->{_left_node}){
	$old_l_balance = $$node->{_left_node}->{_balance};
    }
    if($$node->{_right_node}){
	$old_r_balance = $$node->{_right_node}->{_balance};
    }

    if($$node->{_left_node}){
	$self->rotate_left(\$$node->{_left_node});
    }

    $self->rotate_right($node);

    if($$node->{_left_node}){
	$$node->{_left_node}->{_balance} = -1 * max($old_r_balance, 0);
    }
    if($$node->{_right_node}){
	$$node->{_right_node}->{_balance} = -1 * min($old_r_balance, 0);
    }
    $$node->{_balance} = 0;


    return 1;
}


#
# double_rotate_left
#
# A double left-rotation.  Yes, this is *very* similar code for right and left operations,
# but these subroutines have not been merged to one in the interest of clarity.  After all, according to
# Abelson and Sussman, programs are for humans to read above all, and only incidentally for machines
# to run.    Not that this code is as readable as it could be, of course.
#
sub double_rotate_left
{
   my ($self, $node) = @_;
   my $old_balance = $$node->{_balance};
   my $old_l_balance = 0;
   my $old_r_balance = 0;

   if($$node->{_left_node}){
       $old_l_balance = $$node->{_left_node}->{_balance};
   }
   if($$node->{_right_node}){
       $old_r_balance = $$node->{_right_node}->{_balance};
   }

   if($$node->{_right_node}){
       $self->rotate_right(\$$node->{_right_node});
   }
   $self->rotate_left($node);

   if($$node->{_left_node}){
       $$node->{_left_node}->{_balance} = -1 * max($old_l_balance, 0);
   }
   if($$node->{_right_node}){
       $$node->{_right_node}->{_balance} = -1 * min($old_l_balance, 0);
   }
   $$node->{_balance} = 0;

   return 1;
}


sub is_empty{
    my ($self, $node) = @_;

    if(!$node){
	$node = $self->{_node};
    }

    if(!defined($node->{_obj})){
	return 1;
    }
    return 0;
}




#
# smallest
#
# usage:
#
# my $largest_obj = $avltree->smallest()
#
# Returns the smallest-valued object in the tree
#
sub smallest
{
    my ($self, $node) = @_;
    return $self->extremum($node, 0);
}

#
# largest
#
# usage:
#
# my $largest_obj = $avltree->largest()
#
# Returns the largest-valued object in the tree
#
# Fixed 07/11/09 for version 1.05 by Robert Lehr:
# recursive invocation was called incorrectly
#
sub largest
{
    my ($self, $node) = @_;
    return $self->extremum($node, 1);
}



sub extremum
{
    my ($self, $node, $which_extreme) = @_;

    my $node_dir;

    if($which_extreme eq 0){
	$node_dir = "_left_node";
    }
    elsif($which_extreme == 1){
	$node_dir = "_right_node";
    }
    else{
	croak("Bad extreme type supplied:  must be 0 or 1\n");
    }

    if(!$node){
	$node = $self->{_node};
    }
    my $obj = $node->{_obj};
    my $next_node = $node->{$node_dir};
    if(!$next_node){
	return $obj;
    }
    else{
	my $obj = Tree::AVL::extremum($self, $next_node, $which_extreme);
	return $obj;
    }
}



#
# pop_largest
#
# usage:
#
# my $largest_obj = $avltree->pop_largest()
#
# Removes and returns the largest-valued object in the tree
#
sub pop_largest
{
    my ($self) = @_;
    my ($obj) = $self->delete_largest();
    return $obj;
}

#
# pop_smallest
#
# usage:
#
# my $largest_obj = $avltree->pop_smallest()
#
# Removes and returns the smallest-valued object in the tree
#
sub pop_smallest
{
    my ($self) = @_;
    my ($obj) = $self->delete_smallest();
    return $obj;
}


sub get_key
{
    my ($self, $node) = @_;
    my $get_key_func = $self->{fget_key};
    my $obj = $node->{_obj};
    my $key = $get_key_func->($obj);
    return $key;
}


sub get_data
{
    my ($self, $node) = @_;
    my $get_data_func = $self->{fget_data};
    my $obj = $node->{_obj};
    my $data = $get_data_func->($obj);
    return $data;
}

sub get_height
{
    my ($self, $node) = @_;

    my $depth_left = 0;
    my $depth_right = 0;

    if(!$node){
	$node = $self->{_node};
    }

    if(!$node->{_left_node} && !$node->{_right_node}){
	return 0;
    }
    else
    {
	if($node->{_left_node}){
	    $depth_left = 1 + $self->get_height($node->{_left_node});
	}
	if($node->{_right_node}){
	    $depth_right = 1 + $self->get_height($node->{_right_node});
	}

	return $depth_left < $depth_right ? $depth_right : $depth_left;
    }
}


#
# lookup
#
# usage:  $data = $tree_ref->lookup($object)
#
sub lookup
{
    my ($self,
	$object,
	$cmpfunc) = @_;

    my $node = $self->{_node};

    if(!defined($node->{_obj})){ # no root data yet
	return;
    }
    else{

	while($node){
	    my $node_obj = $node->{_obj};
	    my $get_key_func = $self->{fget_key};
	    my $key = $get_key_func->($node_obj);

	    if(!$cmpfunc){
		$cmpfunc = $self->{fcompare};
	    }
	    my $result = $cmpfunc->($node_obj, $object);
	    if($result == 0){ # element is already in tree- return the key.
		return $key;
	    }
	    elsif($result < 0){ # look into right subtree
		$node = $node->{_right_node};
	    }
	    else{  # look into left subtree
		$node = $node->{_left_node};
	    }
	} # end while
	return;
    } # end else
}


#
# lookup_obj
#
# usage:  $object = $tree_ref->lookup($object)
#
sub lookup_obj
{
    my ($self,
	$object,
	$cmpfunc) = @_;

    my $node = $self->{_node};

    if(!defined($node->{_obj})) # no root data yet
    {
	return;
    }
    else
    {
	while($node){
	    my $node_obj = $node->{_obj};

	    if(!$cmpfunc){
		$cmpfunc = $self->{fcompare};
	    }
	    my $result = $cmpfunc->($node_obj, $object);
	    if($result == 0){ # element is already in tree- return the key.
		return $node_obj;
	    }
	    elsif($result < 0){ # look into right subtree
		$node = $node->{_right_node};
	    }
	    else{  # look into left subtree
		$node = $node->{_left_node};
	    }
	} # end while
	return;
    } # end else
}


#
# lookup_node
#
# usage:  $node_hash = $tree_ref->lookup($object)
#
sub lookup_node
{
    my ($self,
	$object,
	$cmpfunc) = @_;

    my $node = $self->{_node};

    if(!defined($node->{_obj})) # no root data yet
    {
	return;
    }
    else
    {
	while($node){
	    my $node_obj = $node->{_obj};

	    if(!$cmpfunc){
		$cmpfunc = $self->{fcompare};
	    }
	    my $result = $cmpfunc->($node_obj, $object);
	    if($result == 0){ # element is in tree- return the node.
		return $node;
	    }
	    elsif($result < 0){ # look into right subtree
		$node = $node->{_right_node};
	    }
	    else{  # look into left subtree
		$node = $node->{_left_node};
	    }
	} # end while
	return;
    } # end else
}



#
# acc_lookup
#
# usage:    $tree_ref->acc_lookup($object, $partial_cmp_func, $exact_cmp_func)
#
# accumulative lookup, returns a list of all
# items whose keys satisfy the match function for the key for $object.
#
# For example, if used with a relaxed compare function such as:
#
# $word->compare_up_to($arg_word);
#
# which returns true if the argument word is a proper 'superstring' of $word
# (meaning that it contains $word followed by one or more characters)
# this will return a list of all the words that are superstrings of
# $word.
#
sub acc_lookup
{
    my ($self,
	$object,
	$partial_cmpfunc, # partial comparison function to use
	$exact_cmpfunc, # exact comparison function to use
	$node,
	$acc_results) = @_;

    if(!$node){
	$node = $self->{_node};
    }

    # the list of accumulated results
    if(!$acc_results){
	$acc_results = ();
    }

    if(!$partial_cmpfunc || !$exact_cmpfunc){
	return ();
    }

    if(!defined($node->{_obj})){ # no root data yet
	return ();
    }
    else
    {
	while($node){
	    my $node_obj = $node->{_obj};
	    my $get_key_func = $self->{fget_key};
	    my $node_key = $get_key_func->($node_obj);
	    my $partial_cmp = $partial_cmpfunc->($node_obj, $object);
	    my $exact_cmp = $exact_cmpfunc->($node_obj, $object);

	    if($partial_cmp == 0){ # found a match on partial cmp

		if(!$acc_results){
		    @$acc_results = ();
		}
		push(@$acc_results, $node_key);

		if($exact_cmp == 0){ # any other partial matches will be in right subtree
		    $node = $node->{_right_node};
		}
		else{

		    if ($node->{_right_node} && $node->{_left_node}){
			my $rightnode = $node->{_right_node};
			my $leftnode = $node->{_left_node};

			return @$acc_results = (Tree::AVL::acc_lookup($self, $object, $partial_cmpfunc,
									# do not pass in acc_results here
									$exact_cmpfunc, $rightnode),
						Tree::AVL::acc_lookup($self, $object, $partial_cmpfunc,
									$exact_cmpfunc, $leftnode, \@$acc_results));
		    }
		    elsif($node->{_right_node}){
		        my $rightnode = $node->{_right_node};
			@$acc_results = (Tree::AVL::acc_lookup($self, $object, $partial_cmpfunc,
							       $exact_cmpfunc, $rightnode, \@$acc_results));
		    }
		    elsif($node->{_left_node}){
			my $leftnode = $node->{_left_node};
			@$acc_results = (Tree::AVL::acc_lookup($self, $object, $partial_cmpfunc,
							       $exact_cmpfunc, $leftnode, \@$acc_results));
		    }
		    return @$acc_results;
		}
	    }
	    elsif($partial_cmp < 0){ # look into right subtree
		$node = $node->{_right_node};
	    }
	    else{  # look into left subtree
		$node = $node->{_left_node};
	    }
	} # end while
	if(defined(@$acc_results)){
	    return @$acc_results;
	}
	return;
    }  # end else determine whether need to look into left or right subtree
}


#
# acc_lookup_memo
#
# memoized call to acc_lookup
#
sub acc_lookup_memo
{
    my ($self,
	$object,
   	$partial_cmpfunc,  # partial comparison function to use
	$exact_cmpfunc   # exact comparison function to use
	) = @_;

    my $get_key_func = $self->{fget_key};

    my $obj_key = $get_key_func->($object);
    my $acc_lookup_hash_key = $obj_key . $partial_cmpfunc . $exact_cmpfunc;


    if($self->{acc_lookup_hash}->{$acc_lookup_hash_key}){
	my $list = $self->{acc_lookup_hash}->{$acc_lookup_hash_key};
	return @$list;
	}
    else{
	my @results = $self->acc_lookup($object, $partial_cmpfunc, $exact_cmpfunc);
	$self->{acc_lookup_hash}->{$acc_lookup_hash_key} = \@results;
	return @results;
    }
}


#
# get_list_recursive
#
# usage:    @list = $tree_ref->get_list_recursive()
#
# returns an array (list) containing all elements in the tree (in-order).
#
sub get_list_recursive
{
    my ($self, $node, $lst) = @_;

    if(!$node){
	$node = $self->{_node};
    }
    if(!$lst){
	$lst = [];
    }
    if($node->{_left_node}){
	@$lst = Tree::AVL::get_list_recursive($self, $node->{_left_node}, $lst);
    }
    my $obj = $node->{_obj};
    if($obj){
	push(@$lst, $obj);
    }
    if($node->{_right_node}){
	Tree::AVL::get_list_recursive($self, $node->{_right_node}, $lst);
    }

    return @$lst;
}


#
# get_list
#
# usage:    @list = $tree_ref->get_list()
#
# returns an array (list) containing all elements in the tree (in-order).
#
sub get_list
{
    my ($self) = @_;

    my $i = 0;
    my @stack;
    my $node = $self->{_node};

    my @objs = ();

    while(1){
	while($node){
	    $stack[$i] = $node;
	    $i++;
	    $node = $node->{_left_node};
	}
	if($i == 0){
	    last;
	}
	--$i;
	if(defined($stack[$i]->{_obj})){
	    push(@objs, $stack[$i]->{_obj});
	}
	$node = $stack[$i];

	$node = $node->{_right_node};
    }

    return @objs;
}

#
# get_root
#
# returns reference to object at root node.
#
#
sub get_root
{
    my ($self) = @_;
    return $self->{_node}->{_obj};
}

#
# get_size
#
# returns number of objects in the tree
#
#
sub get_size
{
    my ($self) = @_;
    my @list = $self->get_list();
    my $size = @list;

    return $size;
}

#
# iterator
#
# usage:    my $it = $tree_ref->iterator(">") # high-to-low
#           my $it = $tree_ref->iterator("<") # low-to-high
#
# returns an iterator over elements in the tree (in order specified).
#
sub iterator
{
    my ($self, $order) = @_;

    my $first_dir;
    my $second_dir;

    if(!$order){ $order = "<"; }

    if($order eq ">"){ # high to low
	$first_dir = "_right_node";
	$second_dir = "_left_node";
    }
    else{ # low to high (default)
	$first_dir = "_left_node";
	$second_dir = "_right_node";
    }

    my @stack;
    my $i = 0;
    my $node = $self->{_node};

    return sub{
	while(1){
	    while($node){
		$stack[$i] = $node;
		$i++;
		$node = $node->{$first_dir};
	    }
	    if($i == 0){
		last;
	    }
	    --$i;
	    my $obj = $stack[$i]->{_obj};
	    $node = $stack[$i];
	    $node = $node->{$second_dir};
	    return $obj;
	}
	return;
    }
}


sub get_keys_recursive
{
    my ($self, $node) = @_;
    my @keys;

    if(!$node){
	$node = $self->{_node};
    }

    if($node->{_left_node}){
	push(@keys, Tree::AVL::get_keys_recursive($self, $node->{_left_node}));
    }

    push(@keys, $self->get_key($node));

    if($node->{_right_node}){
	push(@keys, Tree::AVL::get_keys_recursive($self, $node->{_right_node}));
    }
    return @keys;
}



sub get_keys
{
    my ($self) = @_;
    my $node = $self->{_node};
    my @stack;
    my $i = 0;
    my @keys;

    while(1){
	while($node){
	    $stack[$i] = $node;
	    $i++;
	    $node = $node->{_left_node};
	}
	if($i == 0){
	    last;
	}
	--$i;
	push(@keys, $self->get_key($stack[$i]));
	$node = $stack[$i];

	$node = $node->{_right_node};
    }
    return @keys;
}


sub get_keys_iterator
{
    my ($self) = @_;
    my @stack;
    my $i = 0;
    my $node = $self->{_node};

    return sub{

	while(1){
	    while($node){
		$stack[$i] = $node;
		$i++;
		$node = $node->{_left_node};
	    }
	    if($i == 0){
		last;
	    }
	    --$i;
	    my $key = $self->get_key($stack[$i]);
	    $node = $stack[$i];
	    $node = $node->{_right_node};
	    return $key;
	}

	return;
    }
}


################################################################################
#
#  Printing functions
#
#
################################################################################
sub print
{
    my ($self, $char, $o_char, $node, $depth) = @_;

    if(!$node && !defined($depth)){
	$node = $self->{_node};
    }
    if(!$depth){ $depth = 0; }
    if(!$o_char){
	$o_char = $char;
    }

    my $key = $self->get_key($node);
    my $data = $self->get_data($node);

    if(!defined($self->{_node}->{_obj})){
	print "tree is empty.\n";
	return;
    }

    if(!defined($key)){
	croak "get_key() function provided to Tree::AVL object returned a null value\n";
    }
    if(!defined($data)){
	$data = "";
    }

    print $char . $key . ": " . $data;
    print ": height: " . $self->get_height($node) . ": balance: " . $node->{_balance} . "\n";

    if($node->{_left_node}){
	my $leftnode = $node->{_left_node};
	Tree::AVL::print($self, $char . $o_char, $o_char, $leftnode, $depth+1);
    }
    if($node->{_right_node}){
	my $rightnode =  $node->{_right_node};
	Tree::AVL::print($self, $char . $o_char, $o_char, $rightnode, $depth+1);
    }
}


sub print_node
{
    my ($self, $node, $char, $o_char) = @_;

    if(!$o_char){
	$o_char = $char;
    }

    my $key = $self->get_key($node);
    my $data = $self->get_data($node);

    if(!defined($key)){
	croak "get_key() function provided to Tree::AVL object returned a null value\n";
    }
    if(!defined($data)){
	$data = "";
    }


    print $char . $key . ": " . $data .  ": balance: " . $node->{_balance} . "\n";
    if($node->{_left_node}){
	my $leftnode = $node->{_left_node};
	Tree::AVL::print_node($self, $leftnode, $char . $o_char, $o_char);
    }
    if($node->{_right_node}){
	my $rightnode =  $node->{_right_node};
	Tree::AVL::print_node($self, $rightnode, $char . $o_char, $o_char);
    }
}

sub print_iterative
{
    my ($self) = @_;
    my @stack;

    my $node = $self->{_node};

    my $i = 0;

    while(1){
	while($node){
	    $stack[$i] = $node;
	    $i++;
	    $node = $node->{_left_node};
	}

	if($i == 0){
	    last;
	}
	--$i;
	print $self->get_key($stack[$i]) . "\n";
	$node = $stack[$i];

	$node = $node->{_right_node};
    }
}

#
# default_cmp_func
#
# default comparison function to use in case none is supplied.
# uses lexical comparator.
#
sub default_cmp_func
{
    my ($obj1, $obj2) = @_;

    if($obj1 lt $obj2){
	return -1;
    }
    elsif($obj1 gt $obj2){
	return 1;
    }
    return 0;
}

sub min
{
    my ($a, $b) = @_;
    return $a < $b ? $a : $b;
}


sub max
{
    my ($a, $b) = @_;
    return $a < $b ? $b : $a;
}


1;
__END__