二叉搜索树与双向链表

 思路：

左指针指向左子树的最大值，右指针指向右子树的最小值。

struct node{
    int value;
    node* left;
    node* right;
}
node* convert(node* root){
    node* pLast = NULL;
    convertNode(root,&pLast);
    node* head = pLast;
    while(head->left != NULL && head != NULL){
        head = head->left;
    }
    return head;
}
void convertNode(node* root,node** pLast){
    if(root == NULL)return;
    node* pCurrnet = root;
    if(pCurrnet->left){
        convertNode(pCurrnet->let,pLast);
    }
    p->left = *pLast;

    if(*pLast != NULL){
        (*pLast)->right = pCurrnet;
    }
    *pLast = pCurrnet;
    if(pCurrnet->right) convertNode(pCurrnet->right,pLast);
}