开始刷leetcode day18：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->NULL

, m = 2 and n = 4,

return

1->4->3->2->5->NULL

.

Note:

Given m, n satisfy the following condition:

1 ≤ m ≤ n ≤ length of list.

Java:

/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

public class Solution {

public ListNode reverseBetween(ListNode head, int m, int n) {

if(head == null || head.next == null || m==n) return head;

int i=1;

ListNode newNode = new ListNode(0);

newNode.next = head;

head = newNode;

while(i<m)

{

newNode = newNode.next;

i++;

}

ListNode pre = newNode.next;

ListNode last = null;

ListNode temp=null;

ListNode end=last;

while(i<=n && pre!=null)

{

temp = pre.next;

pre.next = last;

if(last == null) end = pre;

last = pre;

pre = temp;

i++;

}

newNode.next = last;

end.next = temp;

return head.next;

}

}

注意，需要head = newNode; 并且返回应该是head.next