这道题用C++来写，在本地执行正常，但是使用OJ判断输出结果是空，暂时不清楚原因。代码如下：

class Solution {public:    vector
     
       V;    //中序遍历    void MidTree(TreeNode node)    {        if (&node != NULL)        {            if (node.left != NULL)            {                MidTree(*node.left);            }            V.push_back(node.val);            if (node.right != NULL)            {                MidTree(*node.right);            }        }    }    TreeNode Join(TreeNode* t, int ct)    {        if (ct == V.size() - 1)        {            TreeNode tt = TreeNode(V[ct]);            return tt;        }        TreeNode d = TreeNode(V[ct + 1]);        TreeNode* dd = &d;        TreeNode n = Join(dd, ct + 1);        t->right = &n;        return *t;    }    TreeNode* increasingBST(TreeNode* root) {        MidTree(*root);        TreeNode T = TreeNode(V[0]);        TreeNode* TT = &T;        TreeNode x = Join(TT, 0);        return &x;    }};
     

 保留原有逻辑，修改为C#代码，则通过所有测试，代码如下：

public class Solution    {        public List
     
       V = new List
      
       ();        //中序遍历        public void MidTree(TreeNode node)        {            if (node != null)            {                if (node.left != null)                {                    MidTree(node.left);                }                V.Add(node.val);                if (node.right != null)                {                    MidTree(node.right);                }            }        }        public TreeNode Join(TreeNode t, int ct)        {            if (ct == V.Count() - 1)            {                TreeNode tt =new TreeNode(V[ct]);                return tt;            }            TreeNode d = new TreeNode(V[ct + 1]);                        TreeNode n = Join(d, ct + 1);            t.right = n;            return t;        }        public TreeNode IncreasingBST(TreeNode root)        {            MidTree(root);            TreeNode T =new TreeNode(V[0]);                        TreeNode x = Join(T, 0);            return x;        }    }
      
     

不知是leetcode的判断机制问题，还是我的C++写法的问题。之后还是尽量使用C#吧。