public TreeNode inorderSuccessor(TreeNode root, TreeNode p) {
        TreeNode node = root;
        TreeNode result = null;
        while(node!=null){
            if(node.val>p.val){
                if(result==null || node.val<result.val) result = node;
                node = node.left;
            }else node = node.right;
        }
        return result;
    }