二叉搜索数与双向链表

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    TreeNode *head = NULL; 
    TreeNode *tail = NULL; 
    TreeNode* Convert(TreeNode* pRootOfTree)
    {
        midBL(pRootOfTree);
        return tail;
    }
    // 中序遍历
    void midBL(TreeNode * cur)
    {
        if(cur == NULL) return;
        midBL(cur->left);
        if(head == NULL)
        {
            head = cur;
            tail = cur;
        }
        else
        {
            head->right = cur;
            cur->left = head;
            head = cur;
        }
         midBL(cur->right);

    }
};