Reverse Linked List II

Reverse a linked list from position m to n. Do it in-place and in one-pass.

For example:
Given 1->2->3->4->5->NULL, m = 2 and n = 4,

return 1->4->3->2->5->NULL.

Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.

/**
 * 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;
    }
};