LeetCode Reverse Linked List II

// 先分析   拆成三段    16ms 过大的
 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         // Start typing your C/C++ solution below
13         // DO NOT write int main() function
14         ListNode*preHead,*preEnd,*midHead,*midEnd,*r,*p,*q,*re;
15         
16         int i;
17         
18         
19         preEnd=NULL;
20         p=head;
21         
22         for(i=0;i<m-1;i++)
23         {
24             preEnd=p;
25             p=p->next;
26         }
27         
28         midEnd=p;
29         
30         q=NULL;
31         
32         for(i=0;i<n-m+1;i++)
33         {
34             r=p->next;
35             p->next=q;
36             q=p;
37             p=r;
38         }
39         
40         if(preEnd==NULL)
41         {
42             re=q;
43         }
44         else
45         {
46             re=head;
47             preEnd->next=q;
48         }
49         midEnd->next=r;
50         
51         return re;
52         
53         
54         
55         
56         
57         
58         
59     }
60     
61     
62 };