86. Partition List

 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 {
11 public:
12     ListNode* partition(ListNode* head, int x) 
13     {
14         ListNode *small=head,*big=head,*pre,*rpre;
15         ListNode *res=new ListNode(0);
16         res->next=head;
17         pre=res;
18         while(big!=NULL&&big->val<x)
19         {
20             big=big->next;
21             pre=pre->next;
22         }
23         rpre=pre,small=big;
24         while(small!=NULL)
25         {
26             if(small->val<x)
27             {
28                 rpre->next=small->next;
29                 pre->next=small;
30                 small->next=big;
31                 pre=pre->next;
32                 small=rpre->next;
33             }
34             else
35             {
36                 small=small->next;
37                 rpre=rpre->next;
38             }
39         }
40         return res->next;
41     }
42 };

 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 {
11 public:
12     ListNode* partition(ListNode* head, int x) 
13     {
14         ListNode *psmall=new ListNode(0);
15         ListNode *pbig=new ListNode(0);
16         ListNode *res=psmall,*k=pbig;
17         while(head!=NULL)
18         {
19             if(head->val<x)
20                 psmall=psmall->next=head;
21             else
22                 pbig=pbig->next=head;
23             head=head->next;
24         }
25         pbig->next=NULL;
26         psmall->next=k->next;
27         return res->next;
28     }
29 };