翻转链表 II

/**
* Definition for ListNode
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int x) {
*         val = x;
*         next = null;
*     }
* }
*/
public class Solution {
/**
* @param ListNode head is the head of the linked list
* @oaram m and n
* @return: The head of the reversed ListNode
*/
public ListNode reverseBetween(ListNode head, int m , int n) {
ListNode dummy = new ListNode(0);
dummy.next = head;
ListNode pre = dummy;
for (int i = 0; i < m-1; i++) pre = pre.next;
ListNode start = pre.next;
ListNode next = start.next;
for (int i = 0; i < n-m; i++) {
start.next = next.next;
next.next = pre.next;
pre.next = next;
next = start.next;
}

return dummy.next;
}
}