LeetCode 第92题 反转链表 II

反转链表 II
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。

示例:

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

 1 class Solution97 {
 2 
 3   public ListNode reverseBetween(ListNode head, int m, int n) {
 4     if (head == null || head.next == null || m >= n) {
 5       return head;
 6     }
 7 
 8     ListNode dummyHead = new ListNode(0);
 9     dummyHead.next = head;
10     ListNode pre = dummyHead;
11     ListNode left = dummyHead.next;
12     ListNode right = dummyHead.next;
13 
14     for (int i = 0; i < n - m; i++) {
15       right = right.next;
16     }
17     for (int i = 0; i < m - 1; i++) {
18       pre = left;
19       left = left.next;
20       right = right.next;
21     }
22     for (int i = 0; i < n - m; i++) {
23       pre.next = left.next;
24       left.next = right.next;
25       right.next = left;
26       left = pre.next;
27     }
28 
29     return dummyHead.next;
30   }
31 }