剑指offer-26-二叉搜索树与双向链表

输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。

TreeNode* Convert(TreeNode* pRootOfTree)
    {
        if(!pRootOfTree) return nullptr;
        TreeNode *pre = nullptr;
        TreeNode *root = pRootOfTree;
        ConvertDfs(pRootOfTree, pre, root);
        return root;
    }

    void ConvertDfs(TreeNode *cur, TreeNode *&pre, TreeNode *&root) {
        if(!cur) return;
        ConvertDfs(cur->left, pre, root);
        cur->left = pre;
        if(pre)
            pre->right = cur;
        else 
            root = cur;
        pre = cur;
        ConvertDfs(cur->right, pre, root);
    }