二叉树的遍历

深度优先遍历

class node
{
    public $val;
    public $leftNode;
    public $rightNode;

    public function __construct($val)
    {
        $this->val = $val;
    }

}

$node5 = new node(6);
$node4 = new node(3);
$node3 = new node(5);
$node2 = new node(8);

$node1 = new node(7);
$node1->leftNode = $node3;
$node1->rightNode = $node2;

$node3->leftNode = $node4;
$node3->rightNode = $node5;

function Order($node)
{
    if ($node) {
        $cur = $node->val;
        $left = Order($node->leftNode);
        $right = Order($node->rightNode);
        return $left . '-' . $cur . '-' . $right; // 中序遍历
        /*
         * return  $cur. '-' . $left . '-' . $right; // 前序遍历
         * return $left . '-' . $right . '-' . $cur; // 后序遍历
         * note: 没有的子节点，return的时候注意这个'-'不要哦，我这里为了逻辑清晰就没做判断（不要在意这些细节）
         */
    }
}

echo Order($node1);