力扣-链表-24 两两交换链表中的节点

思路1

设置虚拟节点作为pre，第一个节点是cur，后一个是post，不断更换顺序并且更改好pre的next

代码1

class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        if(!head) return head;
        ListNode* cur = head;
        ListNode* post =  head->next;
        ListNode* dummpy_head = new ListNode();
        dummpy_head->next = head;
        ListNode* pre = dummpy_head;
        while(post){
            ListNode* tmpCur = new ListNode();
            ListNode* tmpPost = new ListNode();
            if(post->next && post->next->next){
                tmpCur = post->next;
                tmpPost = tmpCur->next;
            }else{
                tmpCur = nullptr;
                tmpPost = nullptr;
            }
            pre->next = post;
            cur->next = post->next;
            post->next = cur;
            pre = cur;
            cur = tmpCur;
            post = tmpPost;
        }

        return dummpy_head->next;

    }
};