翻转链表之m,n

https://leetcode.com/problems/reverse-linked-list-ii/
翻转链表第m和第n个之前的元素

 public ListNode reverseBetween(ListNode head, int m, int n) {
        ListNode res = new ListNode(-1);
        ListNode pre = new ListNode(-1);
        ListNode start = new ListNode(-1);
        pre.next = head;
        res = pre;
        int cnt = 0;

        while (head != null) {
            if (cnt < m - 1) {
                pre = pre.next;
                head = head.next;
                cnt++;
                continue;
            }

            if (cnt == m - 1) {
                start = pre;
                pre = pre.next;
                head = head.next;
                cnt++;
                continue;
            }


            if (cnt > m-1 && cnt < n) {
                ListNode tmp = head.next;
                head.next = pre;
                pre = head;
                head = tmp;
                cnt++;
                continue;
            }

            if (cnt == n) {
                //如果放这里，有一个例子可以作证有问题  input：[3,5],m=1,n=2
//                start.next.next = head;
//                start.next = pre;
                break;
            }
        }
        start.next.next = head;
        start.next = pre;
        return res.next;
    }