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.

答案

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public void reverseBetween(ListNode first,ListNode end)
    {
        if(first==end)
        {
            return;
        }
        ListNode prior=first;
        ListNode p=prior.next;
        for(;p!=end;)
        {
            ListNode next=p.next;
            p.next=prior;
            prior=p;
            p=next;
        }
        end.next=prior;
    }
    public ListNode reverseBetween(ListNode head, int m, int n) {
        if(head==null||m==n)
        {
            return head;
        }
        ListNode pHead=new ListNode(0);
        pHead.next=head;
        ListNode prior=pHead;
        ListNode next;
        ListNode first;
        ListNode end;
        int i=0;
        for(i=1;i<m;i++)
        {
            prior=prior.next;
        }
        first=prior.next;
        for(i=m,end=first;i<n;i++)
        {
            end=end.next;
        }
        next=end.next;
        reverseBetween(first,end);
        prior.next=end;
        first.next=next;
        return pHead.next;
    }
}