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 ListNode *partition(ListNode *head, int x) {
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)
15 return head;
16 ListNode * ltail = NULL;
17 if (head->val < x)
18 ltail = head;
19 ListNode *itr = head->next, *last = head;
20 while (itr != NULL){
21 if (itr->val >= x){
22 last = itr;
23 itr = itr->next;
24 continue;
25 }
26 if (last == ltail){
27 ltail = itr;
28 last = itr;
29 itr = itr->next;
30 continue;
31 }
32 last->next = itr->next;
33 if (ltail==NULL){
34 itr->next = head;
35 head = itr;
36 }
37 else {
38 itr->next = ltail->next;
39 ltail->next = itr;
40 }
41 ltail = itr;
42 itr = last->next;
43 }
44 return head;
45 }
46 };
