反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。
    说明:
    1 ≤ m ≤ n ≤ 链表长度。

    输入: 1->2->3->4->5->NULL, m = 2, n = 4 输出: 1->4->3->2->5->NULL

    1. class Solution {
    2.     ListNode successor = null;  //后驱结点
    3.     public ListNode reverseN(ListNode head, int n){
    4.         //base case
    5.         if(n == 1){
    6.             successor = head.next;
    7.             return head;
    8.         }
    9.         ListNode last = reverseN(head.next, n - 1);
    10.         head.next.next = head;
    11.         head.next = successor;
    12.         return last;
    13.     }
    14.     public ListNode reverseBetween(ListNode head, int m, int n){
    15.         //base case
    16.         if(m == 1){
    17.             return reverseN(head, n);
    18.         }
    19.         head.next = reverseBetween(head.next, m - 1, n - 1);
    20.         return head;
    21.     }
    23. }

    https://leetcode-cn.com/problems/reverse-linked-list-ii/solution/bu-bu-chai-jie-ru-he-di-gui-di-fan-zhuan-lian-biao/