思路：添加頭節點，反轉鏈表某個連續部分，206. Reverse Linked List是本題的特殊情況，也可以像本題一樣做，具體見Leetcode 206. Reverse Linked List。

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int x) { val = x; }
 7  * }
 8  */
 9 class Solution {
10     public
 
 ListNode reverseBetween(ListNode head, int m, int n) {
11         if(head == null) return head;
12         ListNode dummy = new ListNode(0);
13         dummy.next = head;
14         ListNode pre = dummy;
15         for(int i = 0; i < m - 1; i++) pre = pre.next;//移動m-1次
16         ListNode start = pre.next;
 
17         ListNode then = start.next;
18         for(int i = 0; i < n - m; i++) {//需要將start後面的n-m個點陸續反轉
19             start.next = then.next;//start的後面指向then的後面
20             then.next = pre.next;//then的後面指向pre的後面，相當於將then插入pre和pre.next之間
21             pre.next = then;//pre的後面是then
22             then = start.next;//
 
完成一個元素的反轉後，then指向下一個準備被反轉（插入pre和pre.next之間）的節點
23         }
24         return dummy.next;
25     }
26 }

Next challenges: Swap Nodes in Pairs Remove Duplicates from Sorted List II Delete Node in a Linked List

Leetcode 92. Reverse Linked List II