1 class Solution { 2 public: 3 ListNode* swapPairs(ListNode* head) { 4 if(head==NULL||head->next==NULL) return head; 5 ListNode prehead(0); 6 prehead.next=head; 7 ListNode *pre=&prehead,*p; 8 while(head&&head->next) 9 { 10 p=head->next; 11 head->next=p->next; 12 p->next=pre->next; 13 pre->next=p; 14 15 pre=head; 16 head=head->next; 17 } 18 return prehead.next; 19 } 20 };