1 class Solution {
2 public void reorderList(ListNode head) {
3 if(head == null) return;
4 if(head.next == null) return;
5 if(head.next.next == null) return;
6 ListNode node1 = head;
7 ListNode node2 = head;
8 while(node2.next != null && node2.next.next != null) {
9 node2 = node2.next.next;
10 node1 = node1.next;
11 }
12 ListNode head2 = node1.next;
13 node1.next = null; //第一半结尾要分开，变成两个单独的linkedlist 这样之后方便点
14 //Reverse head2 list
15 ListNode p1 = head2;
16 ListNode p2 = head2;
17 ListNode p3 = head2;
18 while(p2 != null) {
19 p3 = p3.next;
20 if(head2 == p2) {
21 p2.next = null;
22 p2 = p3;
23 }else {
24 p2.next = p1;
25 p1 = p2;
26 p2 = p3;
27 }
28
29 }
30 head2 = p1;
31
32 ListNode tmp1 = head, head1 = head;
33 ListNode tmp2 = head2;
34 while(tmp2 != null && tmp1 != null) {
35 tmp1 = tmp1.next;
36 tmp2 = tmp2.next;
37 head1.next = head2;
38 head2.next = tmp1;
39 head1 = tmp1;
40 head2 = tmp2;
41
42 }
43 return;
44
45 }
46 }
