class Solution{

     public:

     ListNode *partition(ListNode *head,int x){

         ListNode *dummy=new ListNode(-1);

         dummy->next=head;

         ListNode *pre=dummy,*cur=head;

         while(pre->next&&pre->next->val<x) pre=pre->next;

         cur=pre;

         while(cur->next){

             if(cur->next->val<x){

                 ListNode *tmp=cur->next;

                 cur->next=tmp->next;

                 tmp->next=pre->next;

                 pre->next=tmp;

                 pre=pre->next;

             }else{

                 cur=cur->next;

             }

         }

         return dummy->next;

     }

 };