不同的二叉搜索树2

C++代码：

vector<TreeNode*>res;
    if(n<=0)
    {
        return res;
    }
    else
    {
        res=result(1,n);
        return res;
    }
    }
    vector<TreeNode*>result(int begin,int end)
    {
        vector<TreeNode*>res;
        if(begin>end)
        {
            res.push_back(nullptr);
        }
        for(int i=begin;i<=end;i++)
        {
            vector<TreeNode*>left=result(begin,i-1);
            vector<TreeNode*>right=result(i+1,end);
            for(auto le:left)
            {
                for(auto ri:right)
                {
                    TreeNode*root=new TreeNode(i);
                    root->left=le;
                    root->right=ri;
                    res.push_back(root);
                }
            }
        }
            return res;
        
    }

递归