leetcode JAVA Reverse Linked List II 3.32

Question: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.

/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) {
* val = x;
* next = null;
* }
* }
*/
public class Solution {
public ListNode reverseBetween(ListNode head, int m, int n) {
ListNode back = new ListNode(-1);
back.next = head;
int i = 1;
ListNode temp = back;
while (temp != null && i < m) {
temp = temp.next;
i++;
}
ListNode pre = temp;
while (temp != null && i < n) {
temp = temp.next;
i++;
}
temp = temp.next;
ListNode next = temp.next;
reverse(pre, next);
return back.next;
}

private void reverse(ListNode pre, ListNode next) {
ListNode last = pre.next;
ListNode cur = last.next;
while (cur != next) {
last.next = cur.next;
cur.next = pre.next;
pre.next = cur;
cur = last.next;
}
}
}