1 class Solution {
2 public ListNode reverseBetween(ListNode head, int m, int n) {
3 ListNode node1 = head;
4 // int len = 0; //可以不用加
5 // while(node1 != null) {
6 // len++;
7 // node1 = node1.next;
8 // }
9 // if(len == 1) return head;
10 // node1 = head;
11 ListNode pre = null;
12 for(int i = 1; i <= m - 1; i++) {
13 pre = node1;
14 node1 = node1.next;
15 }
16 ListNode last = head;
17 for(int i = 1; i <= n; i++) {
18 last = last.next;
19 }
20 node1 = head;
21 ListNode record = node1;
22 int count = 1;
23 while(count <= n) {
24 if(count >= m) {
25 record = node1.next;
26 node1.next = last;
27 last = node1;
28 node1 = record;
29 if(count == n) {
30 if(pre != null) { //注意要判断pre是不是null
31 pre.next = last;
32 }else {
33 head = last;
34 }
35 }
36 }else {
37 node1 = node1.next;
38 }
39 count++;
40 }
41 return head;
42
43
44 }
45 }
