> For the complete documentation index, see [llms.txt](https://cai-sen-se.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cai-sen-se.gitbook.io/leetcode/1-200/24.-liang-liang-jiao-huan-lian-biao-zhong-de-jie-dian.md).

# 24. 两两交换链表中的节点

<https://leetcode-cn.com/problems/swap-nodes-in-pairs/>

## 解法一：

一次遍历，用i，j指针表示前后结点对，pre记录i前驱，将i和j交换。

```python
class Solution:
    def swapPairs(self, head: ListNode) -> ListNode:
        Head = ListNode(0)
        Head.next = head
        if not head or not head.next:
            return head
        pre, i ,j = Head, head, head.next
        while i and j:
            #交换
            i.next = j.next
            j.next = i
            pre.next = j
            #更新
            pre = i
            i = i.next
            if i:    #若i非空才有j
                j = i.next
        return Head.next
```


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