二叉樹：二叉樹是每個節點最多有兩個子樹的樹結構。通常子樹被稱作“左子樹”（left subtree）和“右子樹”（right subtree）。
以下是PHP二叉樹實例，請多多指點。
<?php
class treenode
{
public $data;
public $id;
public $left;
public $right;
public function treenode($id=null,$data=null)
{
$this->id=$id;
$this->data=$data;
$this->left=null;
$this->right=null;
}
public function displayss()
{
if($this->left!==null)
{
$this->left->displayss();
}
echo $this->data.' ';
if($this->right!==null)
{
$this->right->displayss();
}
/* echo $this->data.' ';
if($this->left!==null)
{
$this->left->displayss();
}
if($this->right!==null)
{
$this->right->displayss();
} */
}
}
class binarytree
{
private $root;
function binarytree($id=null,$data=null)
{
$this->root=new treenode($id,$data);
}
public function com($old,$new)
{
if($old>$new)
{
return -1;
}
else if($old<=$new)
{
return 1;
}
}
public function addnode($id,$data)
{
if($this->root->data===null)
{
$this->root=new treenode($id,$data);
}
else if($this->root->data!==null)
{
$left=$this->root;
$right=$this->root;
$flag=$this->com($this->root->data,$data);
if($flag<0)
{
while($left->left!==null)
{
if($left->left->data===null)
{
break;
}
$left=$left->left;
}
$left->left=new treenode($id,$data);
}
elseif($flag>0)
{
while($right->right!==null)
{
if($right->right->data===null)
{
break;
}
$right=$right->right;
}
$right->right=new treenode($id,$data);
}
//$this->root=$this->root->addtnode($id,$name);
}
}
public function display()
{
$root=$this->root;
$root->displayss();
//$this->displayss($root);
//print_r($this);
/* if($this->left!==null)
{
$this->left->display();
}
echo $this->data.' ';
if($this->right!==null)
{
$this->right->display();
} */
/* $root=$this->root;
while($root->left!==null)
{
echo 'left:--data:'.$root->left->data.' -->';
$root=$root->left;
}
echo '<br/><br/>';
$root=$this->root;
echo $this->root->data;
echo '<br/><br/>';
while($root->right!==null)
{
echo 'right:--data:'.$root->right->data.' -->';
$root=$root->right;
} */
}
}
$tree=new binarytree();
$tree->addnode(1,'111');
//print_r($tree);
//$tree->display();
echo '<br/>';
$tree->addnode(2,'110');
//print_r($tree);
$tree->addnode(3,'112');
//print_r($tree);
//echo '<br/>';
//exit;
$tree->addnode(4,'109');
$tree->addnode(5,'113');
$tree->addnode(6,'107');
$tree->addnode(7,'114');
$tree->addnode(8,'105');
$tree->display();
?>