//需要注意的就是只用一个pre就能完成交换,一次AC,happy,已经忘记了第一次写链表时候的痛苦,所以说算法没难的,只不过练的欠火候。
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode* swapPairs(ListNode* head) {
if(head == NULL)return NULL;
ListNode *res = new ListNode(0);
res->next = head;
ListNode *pre = res;
while(pre->next && pre->next->next){
ListNode *temp = pre->next->next->next;
pre->next->next->next = pre->next;
pre->next = pre->next->next;
pre->next->next->next = temp;
pre = pre->next->next;
}
return res->next;
}
};