92. Reverse Linked List II（链表部分反转）

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.

 class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
         if(head == null) return head;
         ListNode fakehead = new ListNode(0);
         fakehead.next = head;
         ListNode pre  = fakehead;

         for (int i = 0; i < m-1;i++) pre = pre.next;

         ListNode start = pre.next;
         ListNode then = start.next;

         for(int i = 0 ;i < n -m ;i++){
             start.next= then.next;
             then.next = pre.next;
             pre.next = then;
             then=start.next;
         }
     return fakehead.next;
     }
 }