leetcode 92. 反转链表 II

Posted 2020-11-14 赤云封天

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

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/reverse-linked-list-ii
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

 

 1 class Solution {
 2     public ListNode reverseBetween(ListNode head, int m, int n) {
 3         if (m == n) return head;
 4         ListNode first = new ListNode(-1);
 5         first.next = head;
 6 
 7         ListNode last = first;
 8         ListNode p = first, q = null, t = null, b = first;
 9         for (int i = 0; i < m-1; i++) {
10             b = b.next;
11         }
12         p = b.next;
13         for (int i = 0; i <= n; i++) {
14             last = last.next;
15         }
16         q = p.next;
17         p.next = last;
18         for (; q != last; p = q, q = t) {
19             t = q.next;
20             q.next = p;
21         }
22         b.next = p;
23         return first.next;
24     }
25 }