/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        ListNode * dummyNode =new ListNode(0);
        dummyNode->next =head;
        ListNode * cur =dummyNode;
        while(cur->next!=nullptr&& cur ->next->next!= nullptr){
            ListNode *tmp =cur ->next;
            ListNode *tmp1 =cur->next->next->next;
            cur->next =cur ->next ->next;
            cur->next->next =tmp;
            cur->next->next->next =tmp1;
            cur=cur->next->next;
        }
        return dummyNode->next;
    }
};