二叉搜索树的第k个节点

 ArrayList<TreeNode> arr = new ArrayList<TreeNode>();
    TreeNode KthNode(TreeNode pRoot, int k)
    {
        if(pRoot==null|| k==0){
            return null;
        }
        inOrder(pRoot);
        TreeNode tr = pRoot;
        if(k<=arr.size()){
            tr = arr.get(k-1);
        }else{
            return null;
        }
        return tr;
    }

    public void inOrder(TreeNode root){
        if(root ==null){
            return;
        }
        if(root.left != null){
            inOrder(root.left);
        }
        arr.add(root);
        if(root.right != null){
            inOrder(root.right);
        }
    }