Tree::Node (3pm)

use Tree::RedBlack; my $t = new Tree::RedBlack; $t->insert(3, 'dog'); my $node = $t->node\|(3); $animal = $node->val;

A Tree::RedBlack::Node object supports the following methods:

key ()

Key of the node. This is what the nodes are sorted by in the tree.

val ($)

Value of the node. Can be any perl scalar, so it could be a hash-ref, f'rinstance. This can be set directly.

color ()

Color of the node. 1 for \*(L"red\*(R", 0 or undef for \*(L"black\*(R".

parent ()

Parent node of this one. Returns undef for root node.

left ()

Left child node of this one. Returns undef for leaf nodes.

right ()

Right child node of this one. Returns undef for leaf nodes.

min ()

Returns the node with the minimal key starting from this node.

max ()

Returns the node with the maximal key starting from this node.

successor ()

Returns the node with the smallest key larger than this node's key, or this node if it is the node with the maximal key.

predecessor ()

Similar to successor. \s-1WARNING:\s0 \s-1NOT\s0 \s-1YET\s0 \s-1IMPLEMENTED\s0!!

You can use these methods to write utility routines for actions on red/black trees. For instance, here's a routine which writes a tree out to disk, putting the byte offsets of the left and right child records in the record for each node.

    sub dump {
      my($node, $fh) = @_;
      my($left, $right);
      my $pos = tell $fh;
      print $fh $node->color ? 'R' : 'B';
      seek($fh, 8, 1);
      print $fh $node->val;
      if ($node->left) {
        $left = dump($node->left,$fh);
      }
      if ($node->right) {
        $right = dump($node->right,$fh);
      }
      my $end = tell $fh;
      seek($fh, $pos+1, 0);
      print $fh pack('NN', $left, $right);
      seek($fh, $end, 0);
      $pos;
    }

You would call it like this:

my $t = new Tree::RedBlack; ... open(FILE, ">tree.dump"); dump($t->root,\*FILE); close FILE;

As another example, here's a simple routine to print a human-readable dump of the tree:

sub pretty_print { my($node, $fh, $lvl) = @_; if ($node->right) { pretty_print($node->right, $fh, $lvl+1); } print $fh ' 'x($lvl*3),'[', $node->color ? 'R' : 'B', ']', $node->key, "\n"; if ($node->left) { pretty_print($this->left, $fh, $lvl+1); } }

A cleaner way of doing this kind of thing is probably to allow sub-classing of Tree::RedBlack::Node, and then allow the Tree::RedBlack constructor to take an argument saying what class of node it should be made up out of. Hmmm...

Benjamin Holzman <[email protected]>

Tree::RedBlack