LeetCode：Reverse Linked List II 解法

反转链表的扩展，要求能理解本质，考虑边界情况

class Solution

{

public:

       ListNode* reverseBetween(ListNode* head, int m, int n)

       {

           ListNode* result =  NULL;

           ListNode* p = head;

           ListNode* left = NULL;

           int i = 1;

           for( ; i < m ; i++)

           {

               left = p;

               p = p->next;

           }

           ListNode* subRight = p;

           ListNode* r = NULL;

           for(; i <= n; i++)

           {

               ListNode* q = p->next;

               p->next = r;

               r = p;

               p = q;

           }

           if(left != NULL)

           {

               left->next = r;

               result = head;

           }

           else

           {

               result = r;

               subRight = head;

           }

          

           subRight->next = p;

           return result;

       }

};