二叉搜索树与双向链表

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
class Solution {
public:
    void link(TreeNode *root,TreeNode** last)
        {
        if(!root)
            return ;
        TreeNode* cur=root;
        if(cur->left)
           link(cur->left,last);
        cur->left=*last;
        if((*last)!=NULL)
            (*last)->right=cur;
        *last=cur;
        if(cur->right)
            link(cur->right,last);        
    }
    TreeNode* Convert(TreeNode* pRootOfTree)
    {
        TreeNode * last=NULL;
        link(pRootOfTree,&last);
        while(last!=NULL&&last->left!=NULL)
            last=last->left;
        return last;
    }
};