LeetCode - Refresh - Reverse Linked List II

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode *reverseBetween(ListNode *head, int m, int n) {
12         if (!head || !head->next) return head;
13         int i = 0;
14         ListNode *result = new ListNode(0);
15         result->next = head;
16         ListNode *runner = result;
17         for (i = 0; i < m-1; i++) {
18             runner = runner->next;
19         }
20         i = n-m;
21         head = runner->next;
22         while (i-- > 0) {
23             ListNode *tmp = head->next;
24             head->next = tmp->next;
25             tmp->next = runner->next;
26             runner->next = tmp;
27         }
28         return result->next;
29     }
30 };