leetcode Symmetric Tree 鏡面對稱二叉樹

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

    1
   / \
  2   2
 / \ / \
3  4 4  3

 

But the following [1,2,2,null,3,null,3] is not:

    1
   / \
  2   2
   \   \
   3    3

 

  function isSymmetric($root) {
        return $this->test($root->left,$root->right);
    }
    function test($left,$right) {
        if($left===$right){
            return true;
        }
     if($left==null||$right==null||$left->val!=$right->val){
         return false;
     }
        return $this->test($left->left,$right->right)&&$this->test($left->right,$right->left);
          
    }