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->NULLm = 2 and n = 4,

return 1->4->3->2->5->NULL.

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

 

 1 public class Solution {
 2     public ListNode reverseBetween(ListNode head, int m, int n) {
 3         ListNode safe = new ListNode(-1);
 4         safe.next = head;
 5         ListNode pre = safe;
 6         for(int i=1;i<m;i++){
 7             pre = pre.next;
 8         }
 9         ListNode cur = pre.next;
10         ListNode post = cur.next;
11         for(int i=0;i<n-m;i++){
12             ListNode temp = post.next;
13             post.next = cur;
14             cur = post;
15             post = temp;
16         }
17         pre.next.next = post;
18         pre.next = cur;
19         return safe.next;
20     }
21 }
View Code

 

 

 

 1 public class Solution {
 2     public ListNode reverseBetween(ListNode head, int m, int n) {
 3         if(head==null || m==n) return head;
 4         ListNode safe = new ListNode(-1);
 5         ListNode pre = safe;
 6         safe.next = head;
 7         int step = n-m;
 8         while(m>1){
 9             pre = pre.next;//to the previous of m_th node
10             m--;
11         }
12         ListNode cur = pre.next;
13         ListNode post = cur.next;
14         while(step>0 ){
15             ListNode temp = post.next;
16             post.next = cur;
17             cur = post;
18             post = temp;
19             step--;
20         }
21         ListNode temp = pre.next;
22         pre.next = cur;
23         temp.next = post;
24         return safe.next;
25     }
26 }
View Code

 

posted @ 2014-02-17 02:14  krunning  阅读(118)  评论(0编辑  收藏  举报