Reverse Linked List II

/**
 * 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* newHead = new ListNode(-1);
        newHead->next = head;
        ListNode* p = newHead;
        n = n - m + 1;
        while(--m){
            p = p->next;
        }
        ListNode* cur = p->next;
        ListNode* ptail = cur;
        while (n--) {
            ListNode* pNext = p->next;
            ListNode* curNext = cur->next;
            p->next = cur;
            cur->next = pNext;
            cur = curNext;
            ptail->next = curNext;
        }
        return newHead->next;
    }
};