记录一下 最简单的php创建和遍历二叉树

/** * 二叉树遍历 * @blog<http://www.phpddt.com> */class Node {    public $value;    public $left;    public $right;}//前序遍历，访问根节点->遍历子左树->遍历右左树function preorder($root){    $stack = array();    array_push($stack, $root);    while(!empty($stack)){        $center_node = array_pop($stack);        echo $center_node->value.' ';                if($center_node->right != null) array_push($stack, $center_node->right);        if($center_node->left != null) array_push($stack, $center_node->left);    }}//中序遍历，遍历子左树->访问根节点->遍历右右树function inorder($root){    $stack = array();    $center_node = $root;    while (!empty($stack) || $center_node != null) {             while ($center_node != null) {                 array_push($stack, $center_node);                 $center_node = $center_node->left;             }              $center_node = array_pop($stack);             echo $center_node->value . " ";              $center_node = $center_node->right;         }}//后序遍历，遍历子左树->访问子右树->遍历根节点function postorder($root){        $pushstack = array();        $visitstack = array();        array_push($pushstack, $root);         while (!empty($pushstack)) {            $center_node = array_pop($pushstack);            array_push($visitstack, $center_node);            if ($center_node->left != null) array_push($pushstack, $center_node->left);            if ($center_node->right != null) array_push($pushstack, $center_node->right);        }         while (!empty($visitstack)) {            $center_node = array_pop($visitstack);            echo $center_node->value. " ";        }} //创建如上图所示的二叉树$a = new Node();$b = new Node();$c = new Node();$d = new Node();$e = new Node();$f = new Node();$a->value = 'A';$b->value = 'B';$c->value = 'C';$d->value = 'D';$e->value = 'E';$f->value = 'F';$a->left = $b;$a->right = $c;$b->left = $d;$c->left = $e;$c->right = $f; //前序遍历preorder($a);  //结果是：A B D C E Finorder($a);  //结果是： D B A E C Fpostorder($a); //结果是:  D B E F C A