1 /**
2 * Definition for singly-linked list.
3 * struct ListNode {
4 * int val;
5 * ListNode *next;
6 * ListNode(int x) : val(x), next(NULL) {}
7 * };
8 */
9 class Solution {
10 public:
11 void reorderList(ListNode *head) {
12 // IMPORTANT: Please reset any member data you declared, as
13 // the same Solution instance will be reused for each test case.
14 if (head ==NULL || head->next == NULL){
15 return;
16 }
17 // split the lists to two parts
18 ListNode * lhead=head, *ltail=head, *rhead=head->next; // split the lists to two parts
19 ListNode * itr = head->next;
20 while ((itr!=NULL) && itr->next !=NULL){
21 ltail = ltail->next;
22 rhead = rhead->next;
23 itr = (itr->next)->next;
24 }
25 ltail->next = NULL;
26 //reverse the right part
27 ListNode * last = rhead;
28 itr = rhead->next;
29 while (itr!=NULL){
30 ListNode * tmp = itr->next;
31 itr->next = last;
32 last = itr;
33 itr = tmp;
34 }
35 rhead->next = NULL;
36 rhead = last;
37 //merge the two parts
38 while (lhead!=NULL){
39 ListNode * tmp = lhead->next;
40 if (rhead !=NULL){
41 ListNode * tmp1 = rhead->next;
42 lhead->next = rhead;
43 rhead->next = tmp;
44 rhead = tmp1;
45 }
46 lhead = tmp;
47 }
48 return;
49 }
50 };
