From 8b94306cc6030eb79f2a8376b01f6398d888f7ed Mon Sep 17 00:00:00 2001
From: Eyjan_Huang <81480748+Eyjan-Huang@users.noreply.github.com>
Date: Fri, 20 Aug 2021 03:23:30 +0800
Subject: [PATCH] =?UTF-8?q?=E6=9B=B4=E6=96=B0=200024.=E4=B8=A4=E4=B8=A4?=
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使用变量名使交换的过程更加清晰，而不是使用之前的next.next这样可读性较差
从后往前换

pre = dummy，cur = 2， post=3
dummpy -> 1 -> 2 -> None
先把cur.next = post.next，此时链表为 1 -> None
再 post.next = cur 此时链表为 2 -> 1 -> None, dummpy -> 1 -> None
最后 pre.next = post, 此时为 dummpy -> 2 -> 1 -> None
---
 .../0024.两两交换链表中的节点.md    | 32 ++++++++++++-------
 1 file changed, 20 insertions(+), 12 deletions(-)

diff --git a/problems/0024.两两交换链表中的节点.md b/problems/0024.两两交换链表中的节点.md
index 91e566dd..672b9a8f 100644
--- a/problems/0024.两两交换链表中的节点.md
+++ b/problems/0024.两两交换链表中的节点.md
@@ -160,21 +160,29 @@ class Solution {
 
 Python：
 ```python
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+
 class Solution:
     def swapPairs(self, head: ListNode) -> ListNode:
-        dummy = ListNode(0) #设置一个虚拟头结点
-        dummy.next = head
-        cur = dummy
-        while cur.next and cur.next.next: 
-            tmp = cur.next #记录临时节点
-            tmp1 = cur.next.next.next #记录临时节点
+        res = ListNode(next=head)
+        pre = res
+        
+        # 必须有pre的下一个和下下个才能交换，否则说明已经交换结束了
+        while pre.next and pre.next.next:
+            cur = pre.next
+            post = pre.next.next
             
-            cur.next = cur.next.next          #步骤一
-            cur.next.next = tmp               #步骤二
-            cur.next.next.next = tmp1         #步骤三
-            
-            cur = cur.next.next #cur移动两位，准备下一轮交换
-        return dummy.next
+            # pre，cur，post对应最左，中间的，最右边的节点
+            cur.next = post.next
+            post.next = cur
+            pre.next = post
+
+            pre = pre.next.next
+        return res.next
 ```
 
 Go：