// 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* dummyhead = new ListNode(0);
dummyhead->next = head;
ListNode* current = dummyhead;
while(current->next && current->next->next){
ListNode* tmp1 = current->next;
ListNode* tmp2 = current->next->next->next;
// 指针换向
current->next = current->next->next;
current->next->next = tmp1;
tmp1->next = tmp2;
// 后移
current = current->next->next; // tmp1和current->next->next可相互替换
}
return dummyhead->next;// 此处dummyhead->next不等于head
}
};
