多个指针，让cur倒过来得到结果
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *reverseBetween(ListNode *head, int m, int n) {
ListNode *root = new ListNode(0);
root->next = head;
ListNode *p = root;
for(int i = 0; i < m-1; i++)
p = p->next;
ListNode *h = p;
p = h->next;
ListNode *cur = p->next;
for(int i = m; i < n; i++){
p->next = cur->next;
cur->next =h->next;
h->next = cur;
cur = p->next;
}
return root->next;
}
};