Reverse Linked List II

public class Solution {
    public ListNode reverseBetween(ListNode head, int m, int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ListNode newhead = new ListNode(0);
        
        newhead.next = head;
        
        ListNode runner = newhead;
        for(int i = 0; i < m-1; i++)
        {
            runner = runner.next;
        }
        ListNode premindex = runner;
        ListNode mindex = runner.next;
        
        ListNode pre = mindex;
        runner = mindex.next;
        
        for(int i = 0; i < n - m; i++)
        {
            ListNode tmp = runner.next;
            runner.next = pre;
            pre = runner;
            runner = tmp;
        }
        premindex.next = pre;
        mindex.next = runner;
        return newhead.next;
    }
}