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[Leetcode] 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.

 

Solution:

 1 /** 2  * Definition for singly-linked list. 3  * public class ListNode { 4  *     int val; 5  *     ListNode next; 6  *     ListNode(int x) { 7  *         val = x; 8  *         next = null; 9  *     }10  * }11  */12 public class Solution {13     public ListNode reverseBetween(ListNode head, int m, int n) {14         if(m==n)15             return head;16         ListNode dummy=new ListNode(-1);17         dummy.next=head;18         ListNode pointer=dummy;19         int cnt=m-1;20         while(cnt!=0){21             pointer=pointer.next;22             cnt--;23         }24         ListNode l1,l2,l3;25         l1=pointer.next;26         ListNode last=l1;27         l2=l1.next;28         l3=l2.next;29         cnt=n-m-1;30         while(cnt!=0){31             l2.next=l1;32             33             l1=l2;34             l2=l3;35             l3=l3.next;36             cnt--;37         }38         l2.next=l1;39         last.next=l3;40         pointer.next=l2;41         return dummy.next;42     }43 }

 

[Leetcode] Reverse Linked List II