Reverse Linked List II

需要虚拟个头结点dummy，整个链表分为三个部分，如下图步骤所示：

class Solution {public: ListNode* reverseList(ListNode* head, int SubLength,ListNode*& pThirdHead) {     ListNode* pre = NULL;     ListNode* cur = head;     ListNode* next = NULL;     while(cur != NULL && SubLength--){            next = cur->next;         cur->next = pre;         pre = cur;         cur = next;      }     pThirdHead = cur;     return pre; } ListNode* reverseBetween(ListNode* head, int m, int n) {     if(m == n) return head;     ListNode* Dummy= new ListNode(0);     Dummy ->next = head;     int SubLength = n - m + 1;     ListNode* pFirstTail = PreHead;//左边部分的尾节点     ListNode* pSecondTail = NULL;  //中间部分的头结点、反转后的尾节点     ListNode* pThirdHead = NULL;   //右边部分右边的头结点     int k = m - 1;     while(k-- > 0){         pFirstTail = pFirstTail->next;     }     pSecondTail = pFirstTail->next;    pFirstTail->next = reverseList(pSecondTail, SubLength, pThirdHead);    pSecondTail->next = pThirdHead;    return Dummy ->next; }};